Bang from multibloc valve

[Paul Bunce]

Ok here goes,

I've recently (4 months ago) moved to a new build that has a pressurised hot water tank, this is new to me as all of the other houses I've owned have had combi-boilers.

My issue is as follows;

My hot water is programmed to come on twice a day which it does no problem, but I find once the tank has been heated the first time a "hot" tap is turned on the pressure is very high for a second or two followed by a thud/bang that can be heard throughout the house and I've isolated it to the multibloc valve next to the tank.

Now i understand the hot water tank will increase pressure from heating but its the bang from this valve is concerning me.

Now I could just be getting worked up over nothing and I can call the developer to get a plumber out to investigate but I dont want to be fobbed off with a rubbish excuse like "oh thats normal" when I know there is a wealth of knowledge on here that will let me know one way or another.

 

[ianmcd]

Stop messing around with anything in there, you need a G3 qualified engineer to work on that definitely not a Diy job

 

[Paul Bunce]

At no point have I said I've been doing anything with the system, I wouldn't anyway as its all under warranty, I just want to know know if there is likely to be a fault or not and if there is what the cause could be so I don't get fobbed of by the builders.

 

[Madrab]

Certainly the combination valve shouldn't be thudding/banging at all. There is something that needs to be checked out and you need to get them back in to sort it.

 

[Nozzle]

Expansion vessel lost its expansion space.

Nozzle

 

[Paul Bunce]

So just to close the thread, the diaphragm had failed in the expansion tank.