Unvented heating system noise

[AideyJ]

I've been called out to a loud whining noise on an unvented hot water system. The noise appeared to be from the pump on the return from the hot water so I changed the pump and the related gate valves but still I get this loud whining noise. Any ideas as to what the problem could be?

 

[Gray0689]

Is the noise when heating is on or when got water on
Or when hot tap is turned on

 

[AideyJ]

The noise starts when a tap as been run and coninues once its been turned off

 

[Dannypipe]

Sorry but I have to ask before we go any further, are you qualified to work on unvented systems?

 

[AideyJ]

Sorry but I have to ask before we go any further, are you qualified to work on unvented systems?

Yes I am, Im also Gas Safe registered. Unvented is registered with BPEC

 

[Gray0689]

Ok it's an expansion problem on the domestic side
What make of cylinder
Is it a range tribune

 

[Dannypipe]

Cool. So the noise could be made by a few things. Is it a new system or old. If old I assume the noise is new. Has the system been altered in any way?

Things I found it can be.....

1/The PRV is knackered and over pressurising the system.
2/ A mixer (monoblock tap or even a shower cartridge) is supplied by unbalanced feeds, and the cold is back filling the system, and over pressurising it.
3/ The expansion vessel is flat,punctured.
4/ If Megaflow the air bubble may need to be renewed.
5/ Pipe work is loose, and vibrating.
6/ A valve on the system has a loose jumped and is vibrating. Loo's can often be the culprit.

I'll think of some more.

 

[Dannypipe]

I've got to ask. Why did you change the pump if the noise was occuring when someone ran a tap?

 

[AideyJ]

I've got to ask. Why did you change the pump if the noise was occuring when someone ran a tap?

because the noise appeared to be coming from the pump itself and I thought it may be restricted in some way

 

[Nostrum]

Strainer/non return valve could be restricting/dirty and flow into the cylinder creating noise maybe? Depending on how long it carries on for.

 

[AideyJ]

Not in front of the cylinder right now so dont know the make off hand but it definitely has a external pressure vessel

 

[Gray0689]

If its only when hot tap tired on I'd be guessing expansion
But Danny's list is pretty comprehensive to go bye

 

[AideyJ]

Strainer/non return valve could be restricting/dirty and flow into the cylinder creating noise maybe? Depending on how long it carries on for.

Noise is constant, will go back and check strainer and pressure vessel charge

 

[AideyJ]

The system is approx 4 years old and as never been serviced

 

[Dannypipe]

Orientation of vessle can also apparently make a difference (not been a problem I've come across though.

As can if EV is connected with a flexi hose (flexi hoses often have a smaller internal diameter than a copper tube but are supplied with some cylinders and not seen as an issue by many). I've had a issue with one cylinder and hard plumbing the connection to the EV solved it.

Finally, some vessels have a restriction in the MI connection. The compression to MI union can cause issues (and infact did cause an issue on a cylinder I installed, and the new EV from the manufacturer solved that issue as it was connected straight to a comp fitting. Hard to explain I know.


However these issues would have been from initial installation.

 

[Plamber]

How close is the Pressure redicing valve to the cylinder?

Earlyer in the year I had a squeaky one that could be heard at the cylinder which was a floor above.

 

[lbp plg & htg]

The noise is caused by air in the pipe leading to the expansion vessel. At times of most expansion and the water is run off then the bag flapping over the outlet causes the whining noise.

Different orientation of the vessel, pipe sizing to the vessel can cause this. If vessel can be re-positioned then do so by way of a 22mm x 3/4" FI Tee directly onto the line of pipe, if space is restrictive then put it on the hot draw-off pipe.

 

[BLOD]

Set the ev charge pressure to approx half way between dynamic & static pressures measured at hot tap.

 

[chris watkins]

Set the ev charge pressure to approx half way between dynamic & static pressures measured at hot tap.

Can I ask why BLOD ? I would always set slightly above pressure reducing valve setting !

 

[BLOD]

Had a problem a few years ago on a tribune (vibration noise when a hot tap was opened when cylinder was at max temperature)
The guy I spoke to at Range said if the drop from static to dynamic pressure is to great/fast it can start a vibration. He advised to set ev half way between and it worked perfectly. (I'd already tried numerous other things that didn't sort it).

Have done this ever since and not had any probs.

 

[Dannypipe]

What exactly do you mean BLOD? Interested as I agree a sudden large flow from an outlet can cause noise too.

 

[Dannypipe]

Sorry I have just read your earlier posts. I understand what you're saying. You say that's worked for you in the past?

 

[chris watkins]

Had a problem a few years ago on a tribune (vibration noise when a hot tap was opened when cylinder was at max temperature)
The guy I spoke to at Range said if the drop from static to dynamic pressure is to great/fast it can start a vibration. He advised to set ev half way between and it worked perfectly. (I'd already tried numerous other things that didn't sort it).

Have done this ever since and not had any probs.

This tactic clearly worked for you BLOD in this case but would not normally be used as the capacity of the vessel to take up expansion would be greatly reduced.

System noises are one thing but should not loose site of what an expansion vessel is for.

The setting of the pressure in a EV serving an un-vented hot water system should be set to just above that of the pressure reducing valve, the reason is that we have no control over the water pressures coming into the property if we used existing static or dynamic today, the pressure could change tomorrow, most properties around London now seem to have supply pressure below the normal pressure reducing valve setting of 3.5 Bar.
Setting pressure between static & dynamic would in it self cause water to move in & out of the vessel every time water is used this would lead to early failure.
Most manufacturers of un-vented units with EV use either 12 or 18 Litre vessel (some come pre-charged to 4.1Bar) these are only just large enough to accommodate expansion of there larger models at this pressure reducing it will almost certainly cause pressure relief to operate.

 

[BLOD]

System noises are one thing but should not loose site of what an expansion vessel is for.

I Agree with this.

The setting of the pressure in a EV serving an un-vented hot water system should be set to just above that of the pressure reducing valve, the reason is that we have no control over the water pressures coming into the property if we used existing static or dynamic today, the pressure could change tomorrow, most properties around London now seem to have supply pressure below the normal pressure reducing valve setting of 3.5 Bar.

The pessure will only fluctuate if it's below the rating of the PRV and you're not as likely to get vibration & noise problems with these lower pressures.

Setting pressure between static & dynamic would in it self cause water to move in & out of the vessel every time water is used this would lead to early failure.

Setting the expansion vessel between static & dynamic will surely mean less water movement, hence less vibration or noise ?

Most manufacturers of un-vented units with EV use either 12 or 18 Litre vessel (some come pre-charged to 4.1Bar) these are only just large enough to accommodate expansion of there larger models at this pressure reducing it will almost certainly cause pressure relief to operate.

Range use 12 litre vessels for up to 150l cylinders, 18Litre vessels for up to 250litre cylinders and 24 litre vessels for the larger ones, so they're plenty large enough if 4% is used for expansion.
I believe a system with an expansion vessel charged too high (eg 4.1bar) can also cause premature failure of the expansion valve.

So surely it's better to set the ev pressure right for the system ? (like the manufacturer told me ?)

 

[BLOD]

sorry chris - didn't mean the responces to be so bold :19:

 

[lbp plg & htg]

10 years with a manufacturer going round the country for noise issues - ive told ya's what it is - well almost certainly anyhow.

 

[chris watkins]

No problem BLOD, be as bold as you like :yesnod:.

Range recommend (& supply) there vessels charged to 3Bar same as there PRV's. Checked Stanton & they do the same at 3.5Bar .
Water movement in & out of the EV is all about the air (nitrogen) charge, if you set this at less than the static pressure then water will move into the vessel when the taps are turned off & the pressure rises & out again when the system pressure fall due to the taps being operated (dynamic). This is all without the increase in pressure to the whole system due to water heating (expansion) which now has a lot less room inside the vessel to be accommodated.
A common misconception is that expansion vessels, of any type, can be sized based on 4% of the heated water volume i.e 100 L system would require 4 L vessel.
If you think how they work, with an air charge on outside of the bladder (bag) & water on the inside, for the 4 Litres of heated water to be accommodated all the air would have to be removed from it's space between the outside of the bladder & the vessel wall.
What actually has to happen is that as the system pressure rises so that the water pressure is greater than the air charge water flows into the vessel & the air gets squashed so its pressure increases, more water is heated, more expansion, more water pressures so more water flows into the vessels & so on, until a tap is opened & the system pressure drops back down to normal, then the air pressure inside the vessel is greater than the water pressure so it gets pushed out into the system.

I think what you were being advised by Range to set up was an accumulator, which are just large vessels used for water storage but should not be confused with expansion vessels.

 

[Gray0689]

No problem BLOD, be as bold as you like :yesnod:.

Range recommend (& supply) there vessels charged to 3Bar same as there PRV's. Checked Stanton & they do the same at 3.5Bar .
Water movement in & out of the EV is all about the air (nitrogen) charge, if you set this at less than the static pressure then water will move into the vessel when the taps are turned off & the pressure rises & out again when the system pressure fall due to the taps being operated (dynamic). This is all without the increase in pressure to the whole system due to water heating (expansion) which now has a lot less room inside the vessel to be accommodated.
A common misconception is that expansion vessels, of any type, can be sized based on 4% of the heated water volume i.e 100 L system would require 4 L vessel.
If you think how they work, with an air charge on outside of the bladder (bag) & water on the inside, for the 4 Litres of heated water to be accommodated all the air would have to be removed from it's space between the outside of the bladder & the vessel wall.
What actually has to happen is that as the system pressure rises so that the water pressure is greater than the air charge water flows into the vessel & the air gets squashed so its pressure increases, more water is heated, more expansion, more water pressures so more water flows into the vessels & so on, until a tap is opened & the system pressure drops back down to normal, then the air pressure inside the vessel is greater than the water pressure so it gets pushed out into the system.

I think what you were being advised by Range to set up was an accumulator, which are just large vessels used for water storage but should not be confused with expansion vessels.

I hade the same problem with a range cylinder and they advised the same on an expansion vessel not an accumulator