Unvented System - Groan/Water Hammer when opening hot faucet.

[barki]

Hi


I had an unvenvted system. Its a 210litre high pressure cylinder in the loft with separate expansion vessel.

The boiler is an OilStar oil-fuelled unit downstairs. The system provides DHW to four sinks in the house, and two showers.


The pipework gives out quite a loud groan when we open any of the hot taps - not so much with the shower. It last about 4 or 5 secs then fades away. The noise is closer to a groan than a water hammer sound.


How can I go about sorting this out?


- The pressure in the expansion vessel is fine. 3.5bar. No drips from the cyl overflow.
- Hot water heats and circulates fine, no air in the system as far as I can tell.
- We can't seem to see exactly where the noise comes from....within one of the (stud) walls I think.


Very grateful for anyones advice

I'm reasonably competent as a DIY'er.....butI don't think capable of working on the pressurised cylinder.


Cheers in advance,


Tom

 

[picasso]

Cold water inlet valve would be the usual suspect.

 

[oilboffin]

Pressure too high the expansion valve should blow off at 3bar get a qualified unvented plumber in these things can explode.you have a pressure problem the noise is your tank groaning when you realease the pressure.

 

[dilalio]

It's a callout job because tinkering can lead to bad things happening that may not happen immediately!

 

[barki]

Hi guys - cheers for the responses - Two quite different answers there, is there any way that I can give myself confidence it is/isn't the cyl pressure before spending £££ on calling someone out?

Tom

 

[oilboffin]

You have to be registered to work on them they can be very dangerous.

 

[picasso]

High pressure if you assume the cylinder/prv is 3 bar, lots of cylinders run at 3.5 bar working pressure.

 

[barki]

Sorry, I meant how can I confirm that its a pressure relief/cyl fault, rather than something like the inlet valve that the first poster mentioned?

 

[Steelmasons]

Pressure too high the expansion valve should blow off at 3bar.

Or possibly 6/8 bar dependant on manufacturer..

 

[Steelmasons]

Sorry, I meant how can I confirm that its a pressure relief/cyl fault, rather than something like the inlet valve that the first poster mentioned?

Get someone who's qualified to look @ it , you obviously aren't so leave well alone.

 

[dilalio]

Sorry, I meant how can I confirm that its a pressure relief/cyl fault, rather than something like the inlet valve that the first poster mentioned?

Think of it like 'smelling gas' - all 'you' can do is shut it off at the supply and call a qualified engineer to investigate!
Whatever is causing the issue is part of a 'system' which needs to be thoroughly inspected for safe operation after any component replacement!

 

[Razor900]

Pressure too high the expansion valve should blow off at 3bar get a qualified unvented plumber in these things can explode.you have a pressure problem the noise is your tank groaning when you realease the pressure.

Are you qualified?

Expansion valve does not blow off at 3 bar that's just what the pressure reducing valve is set too. The groaning is almost certainly from the diaphragm in the EV and usually this problem is caused by an unbalanced supply backfeeding the cylinder

 

[thereisawizza]

Have you had the cylinder serviced recently?

 

[barki]

Hi again,

Thanks v much for all the responses

I just sat next to the cyl & EV while my wife operated the tap. It wasn't immediately obvious which the noise was coming from, but with one hand on each, I can certainly feel it coming from the EV, rather than the cyl.

It was last 'serviced' in June (this year) - The EV had actually gone flat, and it was causing a drip from the overflow when the boiler was on. Recharging/pumping the EV to 3.5 bar solved that problem.



We can't actually remember if the groaning stated before or after this, I think after, else I'd have told the plumber who came.



Other than recharging the EV, the service just included a visual look over the tank which took 30 secs.




I note: The PRV on the side of the cyl (on the side of the cyl is stamped T&P relief (temp & pressure?) has 10 BAR written on it....

There is also a 3BAR valve of some kind on the inlet pipe, I assume this is for limiting pressure from the mains.




Cheers again as always, I'll try calling the local plumber tomorrow/Monday,

Tom

 

[thereisawizza]

One things you might want to do, I normally cut a small off-cut of pipe lagging between the expansion vessel and the wall it's bolted to so it doesn't bounce around when you draw water off.