Noise from unvented hot water system

[George Isles]

I know this has been raised before but no one has ever managed to answer and as I have exactly the same problem I am posting again…..my G3 qualified plumber and Gledhill seem baffled by it….they have re-pressurised the tank, changed the PRV, now they are on about installing a shock arrestor but I get the feeling they are just guessing!…. Over the past couple of months the hot water system in my house has started making an incredibly loud reverberation when a hot water tap is opened. I would liken it to the sound of a ruler being twanged on a desk. It is very loud and fades to silence over a period of about 3 or 4 seconds when a hot water tap is opened. It does not do it every time but usually when no hot water has been used for a couple of hours and a bit of pressure has built up in the unvented system. I can feel the vibration in the pipe that leads to the pressure vessel and I can also feel the vibration in the outlet pipe at the top of the tank. I have searched other posts within these forums where a ballcock was identified as the likely source of the problem. This being an unvented system it has no cold water storage. I would be grateful for any suggestions as to what the problem might be or any diagnostics I could try which would be safe for a DIYer on this type of system.

Read more: https://www.diynot.com/diy/threads/loud-vibration-from-unvented-hot-water-tank.542586/#ixzz7Qk2xcOAh

 

[Justin Passing]

Have had 2 where the rubber diaphragm in the expansion vessel sort of reverberated. Felt it with a hand hand on it. Query air trapped on the water side of it, in which case turn it upside down and see if it goes. One of ours did. Try it with almost no precharge pressure, I bet the noise changes.
"The pressure is correct" is not an answer!

 

[Madrab]

Have to agree ... Every time I have come across this issue with unvented cylinders, it has almost always turned out to be an expansion vessel issue or loose pipework.

What are they pre-charging the EV to? What side is the EV on, is it on the Hot Water side or from the control set?

Have they removed the vessel, drained it, checked the pre-charge and then refitted? That has solved this type of issue a couple of times for me.

 

[George Isles]

Thanks, I have queried trapped air on the water side as just before the noise there is a bubbling sound then 5-10 seconds after the tap is opened the reverberation starts, it is defiantly coming from EV tank but I have told as it’s a pressurised system there’s no way air could be on the “wrong” side of he bladder. EV is set to 3bar…..not sure what you mean by “what side” is it on though.

how would i (or more likely the plumber) get the air out of the system of the system?

I should also probably mention that boiler, tank and EV are upstairs so the EV is effectively the highest point on the system.

Thanks for the replies so far

 

[Madrab]

EV is set to 3bar…..not sure what you mean by “what side” is it on though.

Whether it is connected to the cold side from the control valve assembly (PRV/ISO/etc)or if it is connected to the hot water out pipework? Air bubbles can be introduced from the Hot Water side when the water is heating, especially when the EV is higher than the cylinder.

Have they removed the vessel, drained it, checked the pre-charge and then refitted? That has solved this type of issue a couple of times for me.

 

[ianmcd]

post some pics of your setup

 

[dilalio]

You've ruled out any issues with a mixer somewhere I take it?

 

[DP]

I know this has been raised before but no one has ever managed to answer and as I have exactly the same problem I am posting again…..my G3 qualified plumber and Gledhill seem baffled by it….they have re-pressurised the tank, changed the PRV, now they are on about installing a shock arrestor but I get the feeling they are just guessing!…. Over the past couple of months the hot water system in my house has started making an incredibly loud reverberation when a hot water tap is opened. I would liken it to the sound of a ruler being twanged on a desk. It is very loud and fades to silence over a period of about 3 or 4 seconds when a hot water tap is opened. It does not do it every time but usually when no hot water has been used for a couple of hours and a bit of pressure has built up in the unvented system. I can feel the vibration in the pipe that leads to the pressure vessel and I can also feel the vibration in the outlet pipe at the top of the tank. I have searched other posts within these forums where a ballcock was identified as the likely source of the problem. This being an unvented system it has no cold water storage. I would be grateful for any suggestions as to what the problem might be or any diagnostics I could try which would be safe for a DIYer on this type of system.

Read more: https://www.diynot.com/diy/threads/loud-vibration-from-unvented-hot-water-tank.542586/#ixzz7Qk2xcOAh

customer had same issue, was resolved by changing the combination pressure reducing valve

 

[Agile]

I have previously managed to cure this on an apparently correct system by fitting a smaller diameter pipe to the EV. Some of the flexible silver braided pipes seem good for this as their ID is only about 8 mm in many cases. But I am always worried about their safety having been to a few which have burst.

To remove any air on the water side all that is required is to close the inlet valve and drain all the water via a hot tap. Perhaps then slightly pressurise again and loosen a compression fitting on the EV. Then in normal use let all the air out of the air side and see if any water comes out too.

Repressurising can be quite difficult. The only easy( ish ) way is with a double cylinder foot pump and an extension outlet tube to reach the EV with the pump on the floor.

 

[Madrab]

Regin Stirrup pump, comes with a 3m hose, had mine for years now, just the job for high up UV EV's and on the wall boilers. Some say their's failed in no time but looked after mine's at least 5yrs old now.

 

[dilalio]

I've the Makita air pump and air hawk (bought before getting the Makita)

Don't know how good this one is but it's cheap...

https://www.aldi.co.uk/12v-cordless-mini-air-compressor/p/808783560995201

 

[George Isles]

Thanks All,
Still waiting on my plumber calling me back.....think he is ignoring me as he doesn't know how to solve it, no point in a warrunty if you cant fix the problem!

In relation to the potential faulity mixer tap I tried isolating the ones i could, unfortuntly i cannot isolare the bath (this is also a bit strange as the pipe work INCREASES from 15mm to 22mm just before it connects to the tap connecors........is this right? either way there are no isolators on the tap feeds)...Also if it was faulty mixerIi would expect it to happen all the time, the noise only regualry hapens first thing in the morning, just after the hot water has been on.

@Madrab the EV is fed from the cold side, just after the PRV which is low down there is T and the cold pipe travels up and into the bottom of the EV tank.

@DP they tried replacing the PRV a few weeks ago.......worked for about 3 days then noise started again!

Couple of pics of set-up below.....I cant upload video of the noise but happy to e-mail to anyone who thinks they may be able to help.

customer had same issue, was resolved by changing the combination pressure reducing valve

 

[DP]

Use a stick as stethoscope to pin point the noise. This is how I located the defect.

Looking at your setup, you do not have balanced cold feed from that combination valve

Ensure your cold water isolating valve is fully open

Reading you post, I wonder if the issue is due to higher cylinder pressure post cylinder heat up. You said it lasts about a second or 2. When you run a hot tap after the cylinder has heated up, you will have higher pressure at the tap until the combination valve comes into operation.

might be an idea to talk to the makers about this issue

First thing in morning, open the tap gradually and see if that resolved the problem. Only two moving components in that system- EV diaphragm and combination valve pressure reducing parts unless it is a loose pipe that needs clamping but that unlikely as would happen randomly throughout the day

 

[JohnD]

Use a stick as stethoscope to pin point the noise.

or take a great leap forward into the white heat of the 1960's scientific and technological revolution, and invest in an engineer's stethoscope.

 

[Madrab]

I'd still be looking to depressurising the EV, take it off and check the pre-charge pressure with the vessel cold and off the rig and then refit. I'd also be tempted to remove that flexi and try hard piping it.

The noise is usually vibration in the system caused by pressure fluctuations, I've found it can be air in the vessel as it contracts when the water is heated and then expands as the pressure is released when a tap is opened. Do you find you get a little rush of HW to start then it settles? As @DP mentions the PRV can sometimes cause it as it ages and the spring starts to weaken and fluctuations in the system makes the jumper bounce. If that'[s been replaced though then that should rule that out.

Be beside the vessel when you know it going to makes the noise and hold the pipe below the vessel and the base of the EV you may be able to localise it where it coming from.