HELP - Loud Hot Water Noise

[Spinny]

I have had a plumber here today who has repressurised my expansion vessel on an UVC system back up to 3bar.

Unfortuately he left for the day and is now uncontactable but we have a problem.

Every time we run off hot water we are getting a very loud creaking noise from the system.

 

Any help or advice on what may be going on and how to resolve it ?

[John Carroll]

Is this the first "creaking" problem?

Did your plumber de pressurise the UVC before repressurising the EV?

What make of UVC? 

What are the capacities of both the UVC and the EV?, should be labeled on both.

[Spinny]

Thanks for response John.

Yes this is the first creaking/groaning problem.

Did the plumber de pressurise the UVC ? Not sure. I think the water was turned off at one point though, so perhaps.

The UVC is Gledhill Stainless ES 250L, the expansion vessel is a Zilmet, nominal volume 22.

 

The plumber's colleague has since returned. Said the noises were because of some kind of flutter/oscillation from the pressure reduction valve. He let some air out of the expansion vessel to reduce the pressure in it somewhat - didn't have a pressure meter - so not sure of expansion vessel pressure now. This has stopped the loud creaking/groaning noises whenever we ran the hot water.

 

The system has had release through the tun dish on a regular basis over 3 months or so, relieved by running off hot water through the taps when spotted.

 

The plumber is proposing to replace the pressure reduction valve (currently a Caleffi) with a new 28mm pressure reduction valve, having suggested this may help improve flow through the system.

 

Mains pressure is about 3.5 bar.

[John Carroll]

The EV pre pressure should really be set up by measuring the dynamic pressure with a good flow through the cold taps, (to give say 15/20LPM) after the PRV valve or attached to a (cold) tap fed from the balanced cold on the valve set, which yours are, the prepressure should then be set to say 0.2bar below this, this keeps the diaphragm from bottoming out in any circumstances and also positions it better inside in the EV, IMO. This is probably what happened when the pressure was reduced.  It can result in a slightly higher final pressure after a full reheat but this should not be a problem especially since you have a 22L EV on a 252L UVC, 

If the precharge pressure was 3bar then, after a full cylinder reheat to 60C, the final pressure will be 3.93bar, if the dynamic pressure is 2bar and the EV prepressure is set to 1.8bar then the final pressure will be 4.48bar, a little higher, but not a problem and just may cure noisy operation. I advice(d) the few people I know with UVCs to size the EV to 10% of the UVC capacity and set the prepressure to 2bar anyway even if the dynamic pressure is 3bar.