Megaflo UVC - Very Loud Noise When Hot Tap Opened

[techweb]

Hi,

I have noticed that when a hot tap is opened for the first time after a heating cycle (in this case a bath tap), the water flows for a couple of seconds and then there is a very loud noise as can be heard in the video.

Any ideas what it may be? I couldn't deduce the source. The EV was recently checked and pressure increased from 1 to 3 bar per instructions but notably it did this before. I just at that time didn't know the trigger. It hasn't always done this however, probably the last couple of months or so.

Thank you.

 

[techweb]

I'm going to ask my plumber tomorrow but I suspect the PRV on the cold inlet side...

 

[ShaunCorbs]

Internal baffle

 

[techweb]

Internal baffle

My internal baffle was confirmed by Baxi as disintegrated and now have an external EV which was checked recently and increased pressure from 1 to 3 bar per instructions. It did this noise before the EV pressure change.

 

[ShaunCorbs]

My internal baffle was confirmed by Baxi as disintegrated and now have an external EV which was checked recently and increased pressure from 1 to 3 bar per instructions. It did this noise before the EV pressure change.

They would normally supply you with a brand new cylinder as when it degrades it breaks off and can clog stuff so defo shouldn’t be used once identified

 

[techweb]

They would normally supply you with a brand new cylinder as when it degrades it breaks off and can clog stuff so defo shouldn’t be used once identified

They stopped doing that and now fit an EV and strainer. My plumber already put an EV on years ago and I declined the strainer for obvious reasons as it will just get clogged.

Been like it for years. I noticed the bits appearing on kitchen tap mesh but that’s the only tap with mesh in our house. The shower mixes fortunately don’t have them. Most of it has probably worked its way out.

It was only a few weeks ago I contacted Baxi as had no idea on the warranty. They sent an engineer out and he was frank. Strainer a waste of time and that baxi have changed their policy. He did confirm that the cylinder install was very good but at that time I didn’t know what triggered the noise as I would have asked him.

 

[ShaunCorbs]

Well that’s strange as they’ve supplied me one recently I would push more and state there liable for showers and taps as there blocking up also you shouldn’t drink the tap water

 

[techweb]

Well that’s strange as they’ve supplied me one recently I would push more and state there liable for showers and taps as there blocking up also you shouldn’t drink the tap water

To be honest I usually would but I couldn’t replace it without dropping the ceiling. It’s in the loft and must have been fitted before they went in. No way a cylinder would go through the hatch.

In terms of this issue, I’ll see what my plumber says but with the EV being OK, I think it’s got to be either the PRV on inlet or the fill valve.

 

[ShaunCorbs]

Or the diaphragm banging around

 

[techweb]

For completeness, attaching pictures of the installation. I have been told by my plumber and baxi the likely cause is the water inlet control block / PRV. I will be getting this changed shortly.

 

[John.g]

To be honest I usually would but I couldn’t replace it without dropping the ceiling. It’s in the loft and must have been fitted before they went in. No way a cylinder would go through the hatch.

In terms of this issue, I’ll see what my plumber says but with the EV being OK, I think it’s got to be either the PRV on inlet or the fill valve.

If not allready installed, you might ask your plumber to supply and install a pressure gauge on the PRV outlet which should/might have a tapping for it, it would be quite useful for trouble shooting even though it won't give the cylinder pressure after reheating, normally, the EV is sized to 10% of the cylinder capacity so even if the whole cylinder is reheated to 65C, the final pressure should still only rise to 3.9bar, hardly likely to cause any problems when the hot tap is opened, if the PRV is leaking past then the pressure only has to rise to 4.2bar to give a cylinder pressure of 5.8bar on reheating which may cause that noise, even though it shouldn't, on opening the hot tap.
You might just post tne cylinder volume and the EV volume, should be labelled on both.

 

[techweb]

If not allready installed, you might ask your plumber to supply and install a pressure gauge on the PRV outlet which should/might have a tapping for it, it would be quite useful for trouble shooting even though it won't give the cylinder pressure after reheating, normally, the EV is sized to 10% of the cylinder capacity so even if the whole cylinder is reheated to 65C, the final pressure should still only rise to 3.9bar, hardly likely to cause any problems when the hot tap is opened, if the PRV is leaking past then the pressure only has to rise to 4.2bar to give a cylinder pressure of 5.8bar on reheating which may cause that noise, even though it shouldn't, on opening the hot tap.
You might just post tne cylinder volume and the EV volume, should be labelled on both.

Thanks...

So I am doing away with the Calefe PRV block as technically this is not the correct part as technical at Baxi told me. I have ordered the correct parts and my plumber will fit them. Both my plumber and Baxi believe this to be related to the PRV.

Interesting point you mention re the pressure increase.

The cylinder is 210L capacity and it's an 18L EV. This is correct per their sizing charts.

 

[techweb]

@John.g @ShaunCorbs

For the benefit of all that advised, this issue appears to now be resolved following the replacement of the PRV block. The one that was on the system was a Caleffi and not a genuine part (it worked fine for years) so I opted to swap with a very expensive set from Baxi which cost £204.00.

My plumber did the work earlier today, cylinder was drained, he replaced the PRV with the new one and refilled. So far, no noise on tap opening. It got the point it was happening every time the hot tap was opened unless done very very slowly.

One thing I noticed right away was how much more pressure there is when using the hot taps. It wasn't bad before, but now when opened, the pressure is much higher and it tails off after sometime. I actually remember it being like this a long time ago but hadn't notice it drop.

With the old PRV block out, I decided to have a look at the mesh filter. It was impossible to pry it out and I had to force it out by ramming a screwdriver down the edge to lever it out. On one side of the mesh there were some crusty deposits so it could be that this was part of the problem or contributing to it. If a cylinder is serviced annually, I guess these filters are cleared but speaking to my plumber, very few people bother.

I have another adjustable PRV by the main stockcock with gauge (this is also Caleffe), this provides a balanced cold. I may now with the knowledge from the other have this mesh cleaned or may just opt to swap it completely in case it leaks after being dismantled.

Thanks all for your feedback.

 

[techweb]

@John.g @ShaunCorbs

Annoyingly, this issue appears to have resurfaced but not to the same extent as before. The valve was replaced 3 weeks ago and of course as part of this, the system was drained. I am wondering if this will get worse over time and whether draining and refilling makes it go away temporarily. What that does or does not prove I am not sure. Just thinking out loud right now.

 

[Chuck]

The 'rapid banging' does not sound like it's the valve to me. The noise from the valve, turbulence changing in pitch as the pressure rises and the valve closes, sounds normal. The banging sounds to me as though the pipework is moving slightly, as the pressure in the system rises, i.e. 'slip stick' noise.

When you increase the pressure in a pipe three things happen: it stretches lengthwise, increases its circumference, and any bends try to straighten. The more 'expansion volume' air you have in the system (it's a maximum straight after draining and refilling) the slower the rate of pressure rise as the tank fills. If the rate of increase in pressure is low, the pipework has more time to relax as the pressure increases so the 'bangs' can be more numerous and quieter.

Anyway, this is all speculation, but I'd take a look at the way the pipes are clipped.

 

[techweb]

The 'rapid banging' does not sound like it's the valve to me. The noise from the valve, turbulence changing in pitch as the pressure rises and the valve closes, sounds normal. The banging sounds to me as though the pipework is moving slightly, as the pressure in the system rises, i.e. 'slip stick' noise.

When you increase the pressure in a pipe three things happen: it stretches lengthwise, increases its circumference, and any bends try to straighten. The more 'expansion volume' air you have in the system (it's a maximum straight after draining and refilling) the slower the rate of pressure rise as the tank fills. If the rate of increase in pressure is low, the pipework has more time to relax as the pressure increases so the 'bangs' can be more numerous and quieter.

Anyway, this is all speculation, but I'd take a look at the way the pipes are clipped.

Thanks for your input. So in the video, you hear the hot water on the bath being turned on, a few seconds later the noise comes. Now of course, the delay may be the expanded volume of water being drawn out and when water starts passing we have the noise.

 

[John.g]

@John.g @ShaunCorbs

Annoyingly, this issue appears to have resurfaced but not to the same extent as before. The valve was replaced 3 weeks ago and of course as part of this, the system was drained. I am wondering if this will get worse over time and whether draining and refilling makes it go away temporarily. What that does or does not prove I am not sure. Just thinking out loud right now.

If that was a cylinder without a air bubble then a 210L cyl with a 18L EV will/should have a final pressure of 3.95bar after a full reheat and the EV will push the 3.47L of expanded water back into the system when the pressure is falling back to 3.0bar on opening that hot tap which shouldn't cause the slightest problem while doing so, its recommended that the EV precharge is set 0.2/0.3bar lower than the filling pressure to prevent the diaphragm being hard up against the water end and it also supposedly helps in preventing water hammer, so 2.8bar precharge and 3.0bar PRV/filling pressure but how often is that done?.
This cylinder still has the air bubble assuming that the dip tube has not been removed and even with a broken diaphragm should (if no EV) result in a final pressure of ~ 4.28bar on full reheat, now you have two unequal "EVs" which of course will equalise and still further reduce the final pressure to somewhere around maybe 3.3bar, even better one might say but maybe not, the air bubble has now probably disappeared from the cylinder with that broken diaphragm so you could just drain down the whole cylinder and refill it (as you suggested) to restore the bubble and see has the noise again disappeared. As @ShaunCorbs Corbs suggested the broken diaphragm might be slapping up against the top with little or no bubble.
I know people are sick and tired of me saying that I can't understand why a PG isn't installed on all EVs as you then have great information of whats happening.

However, you have a PG on the separate balanced cold, can you note the pressure with no draw off of hot or cold water and then note it again when drawing off HW only (no cold) from that bath? hot tap.

Your first photo shows a proper combination valve set which has now been replaced with this expensive setup. It certainly doesn't look like a combination set, your hand is resting on the PRV? can you post a photo of it please, also further up it shows what looks like the expansion relief valve, can you also post a photo of this, there should also be a non return valve somewhere but maybe part of the PRV.

 

[techweb]

@John.g
Thanks again for your detailed analysis and I get the benefits of using PG's. I will need to do your test / verification on the mains cold PRV when I am back home. I will video it 🙂

The noise / hammer certainly doesn't appear to be coming from the hot outlet / top of cylinder. There is also a NRV fitted here too in order to prevent "possible" back flow to cylinder.

The setup now from bottom to top, consists of the shutoff valve, directly above is the pressure reducing valve and further north the pressure relief valve. These are all genuine Baxi / Megaflo components and expensive I might add.

I took a couple of photos to show Baxi (who I also contacted regarding this). If you need close ups, these can be arranged but they are the correct parts for this system. Ignore the kitchen roll and smart leak detector, I always put these where hidden plumbing work has just been done!

 

[John.g]

@John.g
Thanks again for your detailed analysis and I get the benefits of using PG's. I will need to do your test / verification on the mains cold PRV when I am back home. I will video it 🙂

The noise / hammer certainly doesn't appear to be coming from the hot outlet / top of cylinder. There is also a NRV fitted here too in order to prevent "possible" back flow to cylinder.

The setup now from bottom to top, consists of the shutoff valve, directly above is the pressure reducing valve and further north the pressure relief valve. These are all genuine Baxi / Megaflo components and expensive I might add.

I took a couple of photos to show Baxi (who I also contacted regarding this). If you need close ups, these can be arranged but they are the correct parts for this system. Ignore the kitchen roll and smart leak detector, I always put these where hidden plumbing work has just been done!

Yes, photo below from someone who had/has this "official" baxi installation, at least this pressure reducing valve appears to have a balanced take off port but your one doesn't appear to have one, even though you are providing a form of balanced main externally. I'd like a close up of that PRV, I'm only interested to see the model number to see if its drop tight, baxi might inform you if so, also post the expansion valve setting next time you see it, I think its 8bar?.
I did a few more calcs assuming that the bubble is fully charged, the final pressure after a full reheat should only be 3.2bar (EV+bubble combined) so you should not get any detectable drop in pressure as soon as you draw off HW, but we know that the EV alone is/should be perfectly acceptable at 3.95bar after a full reheat. You might also confirm sometime that the EV is flanged in the middle which will confirm that the diaphragm is sandwitched in the middle which should give smoother movement than the bladder type that are shoved in from the water end.

What about your suggestion of draining/refilling the cylinder?.

 

[techweb]

Thanks @John.g

I will get a picture of the PRV over the weekend but this is the part: Heatrae Sadia Megaflo Inlet Control Kit 95605894 - https://www.cityplumbing.co.uk/p/heatrae-sadia-megaflo-inlet-control-kit-95605894/p/611206?srsltid=AfmBOoqvrKt6UeH5StZIPr7DQQgcyqbS8p9jjVL0fqUWZEJLB_GVXybJ It is 8bar.

One thing is, this does not happen EVERY time the hot tap is opened. It in fact didn't happen after freshly heating the cylinder and running the bath tap for 10 seconds. It however, did a few moments later when re-opening the bath tap again after 2-3 seconds. It is very strange. I also repeated this test later in the day after another heat cycle, opened bath tap for 20 seconds, no noise at all. Closed it, did it again 2 minutes later and got the noise after a couple of seconds of opening the tap. Did it then immediately after 30 seconds, no noise.

I actually want to leave it a little while to see if it get worse. I was worried previously about how violent the noise / hammering was, this time it's quite minimal. Clearly not right but not likely to damage anything in the short term. If it gets worse, it will give me more certainty when draining / refilling the cylinder that this offers short term workaround. It isn't beyond the realms of possibility, that the issue never went away completely with the swap and I just didn't notice it.

Before, it ended up happening literally every time the hot tap was opened.

 

[John.g]

Just read your link now above and there apparently Is a NRV incorporated in the expansion relief valve.
Probably nit picking a bit but a bit strange that the isolating valve is very close coupled to the PRV, saves a few connections I suppose.

• 8 bar pressure relief and non-return valve

 

[techweb]

@John.g

I have taken 3 videos of the external PRV. This is located in a store cupboard in the lean to extension on the outside of our house. The ticking noise seems to come from the water meter, it's always done this.

The first video demonstrates the bath tap being opened for a long period, the second is a shorter period after waiting a couple a minutes and the third after waiting 30 seconds. On the third video at 5 seconds, you can just make out the noise I hear in the loft.

We can see the water initially starts flowing slowly and then increases (presumably as pressure in the cylinder drops / it needs refilling). I don't see anything abnormal here and even in the third, when the noise can be heard, the gauge doesn't show any fluctuations in pressure.

Let me know your thoughts.... I'm still waiting for Baxi to get back to me but they are consulting with their technical team.

 

[John.g]

The mains comes from the right through the (white) flow meter), there is T then where it turns down to a drain cock, is there a line off this going somewhere? to the cylinder PRV??, it also supplies the balanced cold through the PRV so this PG should reflect the mains pressure with the bath HOT tap only open since there is no flow through this PRV and it just opens to try and maintain a (static) pressure of around its setpoint of 3.3bar ish
The pressure drops to almost 2.2bar which means that this is then the maximum dynamic pressure at the cylinder even with its PRV fully open??.
Is my understanding of this correct or is the water first flowing through the balanced cold and then on to the cylinder PRV?

 

[techweb]

The mains comes from the right through the (white) flow meter), there is T then where it turns down to a drain cock, is there a line off this going somewhere? to the cylinder PRV??, it also supplies the balanced cold through the PRV so this PG should reflect the mains pressure with the bath HOT tap only open since there is no flow through this PRV and it just opens to try and maintain a (static) pressure of around its setpoint of 3.3bar ish
The pressure drops to almost 2.2bar which means that this is then the maximum dynamic pressure at the cylinder even with its PRV fully open??.
Is my understanding of this correct or is the water first flowing through the balanced cold and then on to the cylinder PRV?

Thanks for responding…

All water flow travels through the water meter, then the PRV and then onto the cylinder. North of the PRV is everything and this point the cold is effectively balanced. The static pressure fluctuates between 3-4 bar based on what I’ve seen. Dynamic pressure is usually ~2 bar.

 

[John.g]

It then has to pass through the cylinder PRV which effectively is doing nothing as its wide open with a dynamic pressure of 2bar, this IMO should be looked at, the mains should be available right up to the cylinder PRV which is set to 3.0bar, its after this PRV that the balanced cold should be taken, the pressure in the cylinder and the balanced cold will then be truly balanced, Alternatively, if piping too costly/difficult to change, the cold PRV should be relocated on a T taken off the mains, there is then the best possibility of the cylinder PRV actually being in control since its upstream pressure will be at the max available.
I think the EV precharge pressure should be set to 2.0bar, at least this should get the diaphragm to "float" and the final pressure (with PRV still set to 3.0bar) will still be 4.35bar max after a full reheat.

 

[techweb]

It then has to pass through the cylinder PRV which effectively is doing nothing as its wide open with a dynamic pressure of 2bar, this IMO should be looked at, the mains should be available right up to the cylinder PRV which is set to 3.0bar, its after this PRV that the balanced cold should be taken, the pressure in the cylinder and the balanced cold will then be truly balanced, Alternatively, if piping too costly/difficult to change, the cold PRV should be relocated on a T taken off the mains, there is then the best possibility of the cylinder PRV actually being in control since its upstream pressure will be at the max available.
I think the EV precharge pressure should be set to 2.0bar, at least this should get the diaphragm to "float" and the final pressure (with PRV still set to 3.0bar) will still be 4.35bar max after a full reheat.

The PRV on the mains doesn’t actually do anything. The dynamic pressure never goes beyond much above 2 bar and I have to wind it down to actually start restricting the flow. Even if we took mains to the cylinder that one on the inlet would still do nothing… But, of course one day mains pressure could exceed 3 bar and then all of this would have a job to do.

I am not sure if the static pressure ever makes the PRV on the cylinder work albeit momentarily.

A while ago before I even posted here on this issue, the EV pressure was just 1 bar. It was increased to 3 bar when my plumber was doing some other work and I asked him to check. It made no difference to the noise and the EV states charge to be 3 bar.

 

[John.g]

The PRV on the mains doesn’t actually do anything. The dynamic pressure never goes beyond much above 2 bar and I have to wind it down to actually start restricting the flow. Even if we took mains to the cylinder that one on the inlet would still do nothing… But, of course one day mains pressure could exceed 3 bar and then all of this would have a job to do.

I am not sure if the static pressure ever makes the PRV on the cylinder work albeit momentarily.

A while ago before I even posted here on this issue, the EV pressure was just 1 bar. It was increased to 3 bar when my plumber was doing some other work and I asked him to check. It made no difference to the noise and the EV states charge to be 3 bar.

A few points, its relatively easy to see what the static pressure is even if the filter is (and it quite possibly is) partially blocked on the EV, just ensure no hot or cold water draw off, the adjustment screw should be turned clockwise, DOWN, until the press stops rising, once thats established just open a cold tap that gives a good flowrate and even measure it and note the pressure again, you can then get a good idea of the filter condition etc., close the cold tap and open a high flow hot tap and again note the pressure.
The EV precharge pressure of 3bar is not set in stone, its a recommendation based on a assumption that 3 bar can be maintained at any given HW draw off, again, it will just go wide open and the EV will just run at whatever dynamic pressure thats available, say 2.0bar, the EV diaphgram though will be bottomed out and when the HW is shut off then the pressure (if available can rise very suddenly and just perhaps cause some problems. Far better off IMO to establish the dynamic pressure and at least set the EV prepressure say 0.2bar below this but not lower than 1.8bar, even though not essential I would aso set the cylinder PRV dynamically (with HW draw off) by just turning it anticlockwise UP, until the pressure as shown on the cold water PRV just rises a fraction, both the EV and the PRV are then in control and will give the smoothest cylinder operation.
However, IMO, the cylinder should not be fed with two PRVs in series.

 

[techweb]

A few points, its relatively easy to see what the static pressure is even if the filter is (and it quite possibly is) partially blocked on the EV, just ensure no hot or cold water draw off, the adjustment screw should be turned clockwise, DOWN, until the press stops rising, once thats established just open a cold tap that gives a good flowrate and even measure it and note the pressure again, you can then get a good idea of the filter condition etc., close the cold tap and open a high flow hot tap and again note the pressure.
The EV precharge pressure of 3bar is not set in stone, its a recommendation based on a assumption that 3 bar can be maintained at any given HW draw off, again, it will just go wide open and the EV will just run at whatever dynamic pressure thats available, say 2.0bar, the EV diaphgram though will be bottomed out and when the HW is shut off then the pressure (if available can rise very suddenly and just perhaps cause some problems. Far better off IMO to establish the dynamic pressure and at least set the EV prepressure say 0.2bar below this but not lower than 1.8bar, even though not essential I would aso set the cylinder PRV dynamically (with HW draw off) by just turning it anticlockwise UP, until the pressure as shown on the cold water PRV just rises a fraction, both the EV and the PRV are then in control and will give the smoothest cylinder operation.
However, IMO, the cylinder should not be fed with two PRVs in series.

On the cylinder, the genuine Baxi PRV is not adjustable. It is set at 3 bar permanently. Not sure on the PRV is series piece, I can’t see any harm in it and also prior to the mains water getting to our house, the water company will also no doubt have PRVs.

 

[John.g]

Ok, I'll leave it at that as I can't offer any more advice, good or bad, please let us know how you get on.

 

[techweb]

Ok, I'll leave it at that as I can't offer any more advice, good or bad, please let us know how you get on.

Thanks so much for all your input. It’s truly appreciated. If you were local to Northamptonshire, I’d buy you a drink 🙂

 

[techweb]

@John.g I had a thought. I am going to try and test to see if I can reproduce the noise with the inlet valve closed. Now what this would prove, I don’t know but it would rule out anything related to inlet pressures etc.

I am wondering if the NRV on the hot outlet on the top of the cylinder could be causing this.

I’ll give this a go either tomorrow or Friday.

 

[John.g]

@John.g I had a thought. I am going to try and test to see if I can reproduce the noise with the inlet valve closed. Now what this would prove, I don’t know but it would rule out anything related to inlet pressures etc.

I am wondering if the NRV on the hot outlet on the top of the cylinder could be causing this.

I’ll give this a go either tomorrow or Friday.

I would get a pressure gauge installed, you can then monitor what's going on, the NRV could cause a problem but again the supply to the UVC should not be passing through two PRVs IMO.

 

[John.g]

Even though shouldn't make a difference, have you considered remaking the air bubble?, it might smoothen out any pressure spiking, in effect you will be back to the original bubble only with a EV setting of 3.0bar and a cold water pressure of (if) 2.0bar dynbamic.

 

[techweb]

@John.g Well, I can certainly try that, it was done 4 weeks ago when the cylinder was drained to allow replacement of the inlet valve / reducing valve etc. However, remember my bubble is probably useless / non existent as it is slated to have disintegrated and we see pieces of it on the tap mesh in the kitchen.

This afternoon, I shut off the incoming feed into the cylinder and was able to still reproduce the problem. This in my opinion removed the possibility of anything on the inlet side.

 

[John.g]

Did you get much water from the tap when you opened it?.
If the air bubble is still intact, (60 years ago, we had very large cold water UVCs on board ships with a air bubble, NO diaphragm, but had a gauge glass and the level wouldn't change in 3 months or more), and assuming 2bar pressure when you shut the feed, 35L of water would/could flow with the pressure falling from 2bar to 0bar or 26L in falling from 2bar to 1bar, due to the air bubble expanding.

 

[techweb]

Did you get much water from the tap when you opened it?.
If the air bubble is still intact, (60 years ago, we had very large cold water UVCs on board ships with a air bubble, NO diaphragm, but had a gauge glass and the level wouldn't change in 3 months or more), and assuming 2bar pressure when you shut the feed, 35L of water would/could flow with the pressure falling from 2bar to 0bar or 26L in falling from 2bar to 1bar, due to the air bubble expanding.

Oh yes plenty came out and only after a while did the pressure start the drop.

 

[John.g]

You might consider repeating that exercise and measure the EV with a tyre pressure gauge before and after. If the precharge pressure has fallen to 1.0bar then the available vol would still only be 9.0L even if the UVC pressure was 3.0bar on shutting the feed valve, so looks like your bubble is hale and hearty.

 

[techweb]

You might consider repeating that exercise and measure the EV with a tyre pressure gauge before and after. If the precharge pressure has fallen to 1.0bar then the available vol would still only be 9.0L even if the UVC pressure was 3.0bar on shutting the feed valve, so looks like your bubble is hale and hearty.

Since running the test I carried out yesterday with the inlet valve shut, I cannot reproduce the noise once again. I imagine it will rear it's head again in time, but isn't that strange! I can't see how the 10-15 liters of water that got drained out of this whilst testing made any difference. The only thing I wonder is if something is adrift in the tank and moving around until a point it gets stuck / lodged. Pure speculation of course.

 

[ShaunCorbs]

Baffle ?? As 15l would be the top bit of the cylinder where the baffle was / is

 

[techweb]

Baffle ?? As 15l would be the top bit of the cylinder where the baffle was / is

The baffle on mine has started to break up anyway and I have an external EV.

 

[ShaunCorbs]

The baffle on mine has started to break up anyway and I have an external EV.

Yes as stated before this will be your issue

 

[John.g]

Since running the test I carried out yesterday with the inlet valve shut, I cannot reproduce the noise once again. I imagine it will rear it's head again in time, but isn't that strange! I can't see how the 10-15 liters of water that got drained out of this whilst testing mabarde any difference. The only thing I wonder is if something is adrift in the tank and moving around until a point it gets stuck / lodged. Pure speculation of course.

The EV is (presumably) set to 3.0bar and because your dynamic feed pressure is ~ 2.0bar then the EV has no effect since the bubble must still be existing to some degree, it would seem that the bubble is almost completely intact (if charged as per instructions) because it will emit ~ 17L of water (fairly close to what you observed) in falling from 2.0bar to 0bar, if the UVC was refilled without opening any hot tap or the T&PRV then, if this bubble was fully intact it should emit ~ 50L in falling from 2.0bar to 0bar and has now lost ~ 75% of its bubble, it doesn't matter really as your test above does mean that any plastic bits will fall down to the dip pipe end and possibly cause this noise but you don't really care as long as there is no noise when operating "normally".
IMO, if properly set up the UVC PRV should be set to 1.8bar (dynamic pressure is 2.0bar) and the EV precharge pressure set to 1.8bar, Baxi in their wisdom supplied a unadjustable PRV set to 3.0bar so the final pressure after a full reheat with the PRV set to 3.0bar & the EV precharged to 1.8bar will only be 2.76bar after a full reheat (assuming the bubble has finally expired) and still only 4.5bar if the mains pressure increased to 3.0bar or higher, this (4.5bar) is almost exactly the same as the final pressure if the Megaflo was operating as per design conditions.
Baxi also don't seem to place much importance in using a balanced cold since they don't provide one off their PRV, yet the so called (in their view) incorrect combination valve set(s) do, they then install a NRV on the hot outlet which isn't required if the balanced cold is taken from the UVC.

However, it is what it is, but as recommended by most, mains pressure only should be supplied to the UVC PRV., the EV precharge pressure should be checked and IMO reduced to 1.8bar. (only IMO), ideally, the balanced cold should then be teed off downstream of the UVC PRV but before the UVC expansion valve which contains a NRV.

 

[techweb]

Thanks for all the perspective on the pressure and expansion. However, what I can’t get my head around is why after shutting the inlet off and draining 10-15 litres of water whilst reproducing the noise and turning the inlet back on, the noise is mysteriously gone (for now). Of course a part explanation might be that this small / partial drain off recharged the bubble to some extent (if it still exists).

On the subject of the bubble / baffle with mixer strainers getting clogged with the debris from this, I can’t see how it is still working. I am lucky that only my kitchen tap has a strainer and it’s easy to remove. If you look online, people have showers and all sorts that get blocked with this and then it requires a callout from a plumber.

 

[John.g]

You may be better off with no bubble as any debris, if floating, will be up high against the cylinder top, the HW drawoff which is from the end of the dip tube is ~ 25% further down the cylinder but you can remake the bubble if you wish, it will/may not long as last as with a intact baffle but you can certainly remake it.

 

[techweb]

@John.g I've noticed the noise has returned but I am satisfied to have ruled out expansion.

When this video was taken a significant amount of hot water (half a bath) had been used since the last heating cycle and testament to this fact is the EV was cold to the touch as was the pipe between that and the cylinder.

I am leaning towards thinking either a dodgy NRV (single check at the top of the cylinder) or something within the cylinder. Interestingly, this time the noise was much louder and echo's. Any feedback welcomed. I've decided the next course of action is the NRV.

 

[techweb]

@John.g I've noticed the noise has returned but I am satisfied to have ruled out expansion.

When this video was taken a significant amount of hot water (half a bath) had been used since the last heating cycle and testament to this fact is the EV was cold to the touch as was the pipe between that and the cylinder.

I am leaning towards thinking either a dodgy NRV (single check at the top of the cylinder) or something within the cylinder. Interestingly, this time the noise was much louder and echo's. Any feedback welcomed. I've decided the next course of action is the NRV.

Interestingly, if you watch the video zoomed in, you can see the tundish and pipe near it move / vibrate with this noise. I am even curious if this could be the PRV but I can't think of any reason why it would do this. No water residue in tundish.

 

[techweb]

I’ve decided that I’m going to remove the NRV on the top of the cylinder and replace the T&P valve whilst I have the plumber out.


After that the only part not replaced will be the EV.

 

[John.g]

Did that noise occur while drawing off HW and stop when the HW draw off stopped?.
Get the plumber to recheck the EV precharge pressure, it was down to 1.0bar previously? so if not set to that initially then must be losing pressure, it could possibly be at 0bar in which case there will be no movement of water in the pipe, hot or otherwise., and the expansion is just been taken up by the bubble which was recently remade, of course that was the original design, removing that NRV is probably no harm.
I am a bit surprised that baxi didn't make a song and dance about not having the balanced cold supplied from between the PRV and the expansion valve, maybe thats why they install a NRV on the hot outlet.
What about reclipping the pipework?.

 

[techweb]

Did that noise occur while drawing off HW and stop when the HW draw off stopped?.
Get the plumber to recheck the EV precharge pressure, it was down to 1.0bar previously? so if not set to that initially then must be losing pressure, it could possibly be at 0bar in which case there will be no movement of water in the pipe, hot or otherwise., and the expansion is just been taken up by the bubble which was recently remade, of course that was the original design, removing that NRV is probably no harm.
I am a bit surprised that baxi didn't make a song and dance about not having the balanced cold supplied from between the PRV and the expansion valve, maybe thats why they install a NRV on the hot outlet.
What about reclipping the pipework?.

Thanks for your continued input…

The sound this time (not sure if you heard the latest video) happens a few seconds after starting to draw hot water. Probably around 4-6 seconds.

I will ask plumber to check EV pressure again but remember this happened when it was at 1 bar and also at 3bar.

Baxi were fine with the setup. The balanced cold comes by virtue of the PRV set at 3bar on the incoming cold water main and the NRV on hot side as belt and braces.

I do worry that this vibration / hammer may cause something to fail / burst, although my plumber assures me it won’t, but concedes this needs to be resolved. In terms of clipping pipes, everything is well clipped apart from the pipes that run vertically to the cylinder. Not much that can be done with those.

 

[techweb]

@John.g
OK, so my plumber came today and for the first time I reproduced it with him in the loft next to the cylinder.

I had him out to replace the NRV, T&P and EV. Figured I'd make sure everything had been done but after hearing the noise he told me it is definitely coming from inside the cylinder. On another group a plumber suggested that the breakup of the baffle can cause this noise as it catches / releases. Anyway, I've contacted Baxi to get a replacement.

 

[ShaunCorbs]

Yep seen it many times

 

[techweb]

Yep seen it many times

I wasn’t aware the baffle making this noise was common prior.

 

[ShaunCorbs]

I wasn’t aware the baffle making this noise was common prior.

Guess you missed post 3

 

[techweb]

Guess you missed post 3

Very good point. I just wasn’t aware that you meant it made the noise. Thinking about it now. I feel a bit silly.

 

[John.g]

Probably influenced by the ceiling having to come down to install new one, post #8.

 

[techweb]

Probably influenced by the ceiling having to come down to install new one, post #8.

Interestingly, my plumber did some measurements whilst he was here and it can come out but the hatch will need to be removed so not too much damage / disruption.

 

[John.g]

As a aside, I see OSO say you can increase their UV cylinder capacity by removing the dip tube and installing a EV, assuming that these too have a baffle, then I wonder why this isn't causing noise if floating about, albeit, in one piece, maybe because the cylinder is now full to the top, no air bubble. If the megaflow could be confirmed full, air bubble completely depleted, would the pieces of plastic float and be hard up against the top of the cylinder with no noise??. also no bits of plastic might flow out as the dip tube end is a 1/4 way further down the cylinder.

Also I see that the OSO effectively charges the bubble with a empty cylinder which should give a 5 fold increase in the air bubble to ~ 50L vs 10L in a 210L cylinder after a full reheat, maybe they don't have a baffle.

 

[techweb]

As a aside, I see OSO say you can increase their UV cylinder capacity by removing the dip tube and installing a EV, assuming that these too have a baffle, then I wonder why this isn't causing noise if floating about, albeit, in one piece, maybe because the cylinder is now full to the top, no air bubble. If the megaflow could be confirmed full, air bubble completely depleted, would the pieces of plastic float and be hard up against the top of the cylinder with no noise??. also no bits of plastic might flow out as the dip tube end is a 1/4 way further down the cylinder.

Also I see that the OSO effectively charges the bubble with a empty cylinder which should give a 5 fold increase in the air bubble to ~ 50L vs 10L in a 210L cylinder after a full reheat, maybe they don't have a baffle.

As far as I am aware, the Megaflo is not something that has this feature or can be dismantled. For example they won’t replace the bubble / baffle. This would make sense to be serviceable in the field.

 

[John.g]

As a aside, I see OSO say you can increase their UV cylinder capacity by removing the dip tube and installing a EV, assuming that these too have a baffle, then I wonder why this isn't causing noise if floating about, albeit, in one piece, maybe because the cylinder is now full to the top, no air bubble. If the megaflow could be confirmed full, air bubble completely depleted, would the pieces of plastic float and be hard up against the top of the cylinder with no noise??. also no bits of plastic might flow out as the dip tube end is a 1/4 way further down the cylinder.

Also I see that the OSO effectively charges the bubble with a empty cylinder which should give a 5 fold increase in the air bubble to ~ 50L vs 10L in a 210L cylinder after a full reheat, maybe they don't have a baffle.

For interest,
Oso technical inform that there is no baffle in their cylinders, so it seems that repressurizing a almost empty cylinder without a baffle will give, presumably, the same times between recharging as repressurizing 25% of the vol of a baffled cylinder.