Clunk Noise from Hot Water Tank Cupboard

[tek_architect]

Hi Everyone,

I'm looking for some advice as to what the loud clunking noise is that occurs when the cold water feed is activated in my house - either from a tap, toilet, washing machine, dishwasher etc.

The symptoms seem to occur if the cold water has not been accessed for an hour or so. An example would be, first thing in the morning, turn on the cold tap (even just a trickle) and there's a bit of a surge in water flow and then a clunk noise from the hot water tank cupboard. The water flow then reverts to a more normal flow. This occurs if you turn any cold tap on a tiny bit or full. This occurs if you flush the loo, when the dishwasher fills or if the washing machine fills.

We have an unvented Santon hot water system. I believe it's a Premier type tank, about 250 litres. The tank also has an expansion vessel. I think the noise is coming from the gubbins below plinth where the tank sits. There's all sorts of pipework, valves etc hidden in there. It's a newish build house - the system has been in for about 4 years.

I don't think it's water hammer as it doesn't happen when you switch the tap off or for example when the dishwasher stops filling.

I've tried things like turning all the cold taps on in the house - thinking it might be some kind of airlock. You can all laugh if you want!

The incoming mains feed to the house has a grey Caleffi pressure reducing valve with replaceable filter. It says 3 Bar on it. There is a + and - on it that appears adjustable with a philips screwdriver.

I just want to know whether the source of the problem could be either from the incoming mains or if it lies in something wrong in the hot water tank cupboard. Looking to either fix myself or know what I'm talking about when I call out a professional.

Any help would be really appreciated.

Regards

David

 

[Keefy]

Turn your cold tap on at the kitchen sink right now and turn it off again and let us know if you hear it.

 

[Best]

Have you had the unit serviced by someone qualified?
You shouldn't really touch any parts relating to the unit yourself.

 

[Resolute]

How long has the noise been happening?

 

[tek_architect]

How long has the noise been happening?

About 6 months it's been happening. The expansion tank was replaced by British Gas for another issue - water was coming from the outflow pipe (I think it's called) - not the condensate pipe.

I mentioned the clunking noise to them but they weren't interested. I was hoping that replacing the expansion vessel would fix that issue too but it didn't. I was waiting until winter was well and truly over before getting anything related to the water system in the house looked at. Now the clunk is just bugging me.

Yes - it's still clunking - twice as a matter of fact when the dishwasher was on a short time ago.

Regards

 

[tek_architect]

Have you had the unit serviced by someone qualified?
You shouldn't really touch any parts relating to the unit yourself.

Once the boiler manufacturer guarantee expired (2 yrs) we've had the boiler and hot water system serviced maintained by British Gas.

Cheers

 

[Keefy]

Yes - it's still clunking - twice as a matter of fact when the dishwasher was on a short time ago.

Regards

Is your dishwasher cold feed only?

 

[Sparkgap]

Non-return valve shutting? If you are getting an initial surge what sort of pressure is the PRV set at or allowing through? Could be you're getting higher pressure building up over a period of time through the PRV then when you open a tap the system pressure drops to what it should be. Then when that happens the cold feed to the hot water cylinder is higher and tries to flow back and the HWS check valve shuts causing the clunk. Rough guess. I assume it doesn't happen if you open the HW tap slightly first?

 

[tek_architect]

Is your dishwasher cold feed only?

Yes - it's cold feed only.

Cheers

 

[tek_architect]

Non-return valve shutting? If you are getting an initial surge what sort of pressure is the PRV set at or allowing through? Could be you're getting higher pressure building up over a period of time through the PRV then when you open a tap the system pressure drops to what it should be. Then when that happens the cold feed to the hot water cylinder is higher and tries to flow back and the HWS check valve shuts causing the clunk. Rough guess. I assume it doesn't happen if you open the HW tap slightly first?

You are spot on. If I turn on the hot tap for a few seconds and then flush the toilet or turn on the cold tap - then no clunk!

What do you recommend I do here then? Is it something that a non-professional could do or do you recommend getting a plumber in? When you talk about the PRV do you mean the Caleffi device I mention in my initial post? When you mention HWS check valve do you mean some device below the hot water tank?

Sorry for the amateur type questions. I work in IT and am clearly not a plumber but I do like to understand and try to fix the root cause of something.

Regards

 

[Keefy]

Yes - it's cold feed only.

Cheers

Then I'm thinking it's just a loose jumper on your incoming stop tap. Get it changed and see if that fixes the problem.

 

[tek_architect]

Then I'm thinking it's just a loose jumper on your incoming stop tap. Get it changed and see if that fixes the problem.

Thanks for that advice too. Is that a big job? Again - if you read my reply to sparkgap I'm clearly no plumber and work in IT 🙂

 

[Keefy]

Thanks for that advice too. Is that a big job? Again - if you read my reply to sparkgap I'm clearly no plumber and work in IT 🙂

Turn off the water out in the street, drain down and replace. Not a hugely difficult job (in theory) and at best you'll cure the problem, at worst you'll have a new stoptap and know the problem lies elsewhere if that makes no difference. Got to start eliminating the possibilities somewhere.

Also, I'd recommend getting a plumber to do it if you haven't got a lot of experience.

 

[lame plumber]

if you an architect you can afford a plumber🙂

 

[tek_architect]

Turn off the water out in the street, drain down and replace. Not a hugely difficult job (in theory) and at best you'll cure the problem, at worst you'll have a new stoptap and know the problem lies elsewhere if that makes no difference. Got to start eliminating the possibilities somewhere.

Also, I'd recommend getting a plumber to do it if you haven't got a lot of experience.

Thanks for the advice. Much appreciated. One more thing - this clunk noise - is it going to damage anything in the system at the moment in your opinion? By that I mean could I end up with a leak or a burst pipe after one too many clunks!!

Cheers

 

[tek_architect]

if you an architect you can afford a plumber🙂

Ha Ha! An IT Technical Architect though. Yep - I can afford a plumber - you're right.

Cheers

 

[Keefy]

Thanks for the advice. Much appreciated. One more thing - this clunk noise - is it going to damage anything in the system at the moment in your opinion? By that I mean could I end up with a leak or a burst pipe after one too many clunks!!

Cheers

I shouldn't think so but I wouldn't like to ignore it long enough to find out.

That's if it is a loose jumper.

 

[Sparkgap]

You are spot on. If I turn on the hot tap for a few seconds and then flush the toilet or turn on the cold tap - then no clunk!

What do you recommend I do here then? Is it something that a non-professional could do or do you recommend getting a plumber in? When you talk about the PRV do you mean the Caleffi device I mention in my initial post? When you mention HWS check valve do you mean some device below the hot water tank?

Sorry for the amateur type questions. I work in IT and am clearly not a plumber but I do like to understand and try to fix the root cause of something.

Regards

My thought would be why do you have a PRV (yes, the Caleffi device) on the incoming mains? Is the water pressure in your area particularly high? According to the manufacturer's blurb the factory setting is 3 Bar. According to the Santon instructions the PRV on the HW cylinder is set at 3.5Bar, so with the mains pressure lower than that it isn't doing a lot and the check valve built into it would be giving you the clunk when the water tries to flow backwards!
An easy suggestion would be to adjust the pressure off the Caleffi unit until it is above the setting for the HW cylinder, so about 4 Bar. Is there a gauge on the PRV? What model is it?

 

[happyflyer]

Then I'm thinking it's just a loose jumper on your incoming stop tap. Get it changed and see if that fixes the problem.

keefy,

I am like you I would go to that first, they are a pest sometimes, but this only started 6 months back, still it might be, still lots of bits and pieces that might trigger it, sometimes cracking the stop tap down will cure it if it the jumper in the stop tap, lessens the gap between the seat and the washer.

Hay well all sent to try us Keefy, nice to have brains , I have never used mine, " now have I " I can't remember now!!!:38:

 

[Best]

Oddly, sometimes the washer in the stopcock can have same effect. Haven't a clue why, but a new washer is also recommended to rule that out.

If the stopcock is turned nearly off, you can get a hammer noise when taps are turned on.

 

[happyflyer]

The washer in the stop tap can act like a hydraulic ram pump, once it starts moving, sometimes it just doesn't know when to stop, in other words it has no brain, it needs a little help, a long time ago we would take them out and hammer up the shaft until you had to bang them back into the hole, this would then make them useless as a NRV, did they ever perform such a duty, one will never know.

Tony

http://www.youtube.com/watch?v=u2nGlnMNXrw

BTW water hammer on the ram pump is much slower than that caused by household plumbing fitting

 

[tek_architect]

keefy,

I am like you I would go to that first, they are a pest sometimes, but this only started 6 months back, still it might be, still lots of bits and pieces that might trigger it, sometimes cracking the stop tap down will cure it if it the jumper in the stop tap, lessens the gap between the seat and the washer.

Hay well all sent to try us Keefy, nice to have brains , I have never used mine, " now have I " I can't remember now!!!:38:

I turned the stop tap clockwise a couple of turns as it was fully open. That was last night. Thought it had made a difference but got a clunk this morning unfortunately.

Cheers

 

[tek_architect]

My thought would be why do you have a PRV (yes, the Caleffi device) on the incoming mains? Is the water pressure in your area particularly high? According to the manufacturer's blurb the factory setting is 3 Bar. According to the Santon instructions the PRV on the HW cylinder is set at 3.5Bar, so with the mains pressure lower than that it isn't doing a lot and the check valve built into it would be giving you the clunk when the water tries to flow backwards!
An easy suggestion would be to adjust the pressure off the Caleffi unit until it is above the setting for the HW cylinder, so about 4 Bar. Is there a gauge on the PRV? What model is it?

To be honest I'm not sure if the water pressure is particularly high in the area. We've had the house from new for 4 years so this was attached inline to the stop valve under the utility room sink. It doesn't have a guage. There's no model number I can see on it but it looks like model 5334 based on what I can see on the caleffi site. If I increased the pressure in the house could that not put the pipe work at risk? Is there anyway to adjust the pressure of the santon? Or is that too dangerous for someone unqualified and not feasible because it has to run at 3.5 bar?

the 5334 details on the site says you can attach a pressure guage but I can't fathom out how.

cheers