Boiler de-pressurising, no leaks visible

AtifMalik

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Hi
I got a new boiler last year (valiant combi), and since had 9 months of internal refurbishments done including all new radiators, many newly positioned radiators and subsequent pipework especially in ensuite bathrooms. Had no problem until few weeks after the work was finished that I found my boiler shut from low pressure. After topping up, I noticed it would de-pressurise within 2 weeks, and hence asked my builder to investigate. He and his plumber have investigated our whole house and we can't find a leak, then the speed at which it de-pressurises has got faster and faster, to 1 week, then every few days and now every 24 hrs. My builder has investigated several times but is at a loss, his plumber has said boiler is working fine with no internal leak, and there is no leak to be found. We did notice water coming out of the over pressurising pipe from the boiler but builder thought that was normal.
Would really appreciate any thoughts and/or advice what to investigate next, before my boiler completely breaks.

bouicca21

When that happened to me, the cause was a leak under the floor. The pipe work was barely two years old but there was a bad join.

Cardew

We did notice water coming out of the over pressurising pipe from the boiler but builder thought that was normal.

Welcome to the forum.

Why would the symptom above be normal?

I suggest you contact the technical helpline of Vaillant.

https://www.vaillant.co.uk/homeowners/technical-help/index.en_gb.html

In fact the plumber should have contacted them if he can't find the fault, it is part of the warranty.

marcarm

We had this, had a company out who couldn't find the issue and thought the next step would be to replace the whole heating system.

Got a second opinion from someone else, saw the exact same issue with the exact same boiler just a few weeks ago and it was the heat exchanger in the boiler that was covered in limescale as we live in a hard water area.

Replaced it at a cost of about £600 and it's been fine ever since.

Hasbeen

Boiler depressurises because it is loosing water.

Builder and plumber cannot find leak but builder notices water escaping from pressure valves exterior pipe.

Thinks this is normal?? And obviously plumber is not a boiler engineer?

Once pressure valves activate they normally never reseat very well and discharge only gets worse.

As Cardew advises if under warranty contact MFG, if not get a qualified Gas safe fitter in to inspect/test boiler.

AtifMalik

we did have some pipework on the ground floor but with the boiler depressurising faster and faster, is that normal to be from a leak? esp as ground floor pipework was cemented over?

Ectophile

AtifMalik wrote: »

we did have some pipework on the ground floor but with the boiler depressurising faster and faster, is that normal to be from a leak? esp as ground floor pipework was cemented over?

Was the pipework covered with anything before cementing? If not, the chemicals in the cement can corrode the pipe.

Rodders53

Discharge from the over-pressure pipe (as #5 states, the valve may not re-seat properly after)...

Suggests to me the expansion vessel may have lost pressure or even be inadequately sized for the new radiator and/or pipework volume? This could lead to the same result of water leaking from that overflow pipe?

Only time I ever had water leaking from my system boiler's over-pressure was due to the boiler's pressure vessel needing pumping back up. {Which I did myself.} However when that happened the boiler pressure when running was higher than normal, and when the boiler was cold very low... The boiler manuals (you should have been left these) will give an indication of normal pressure readings to expect / set during installation / operation.

Additionally, the boilers inbuilt pressure vessel may not have enough expansion volume to cope with a larger amount of water in the system due to the changes (and extras?) you have had installed? Again the manual indicates when additional pressure vessels will be needed, based on volume of water in the installation.

I'd suggest getting in touch with the original installer of the boiler for advice and possible rectification. {Although as others have messed with the installation, it may be any boiler manufacturer warranty has been invalidated, if not on the maker's approved / qualified register.}

Hasbeen

As said before boiler is loosing pressure because water is leaking through pressure relief valve!

That is first port of call.

Contact MFG or get someone qualified to check boiler!

Edvin_Paus

Expansion vessels are found in most boilers, especially, and are needed to cope with the extra water created by expansion during the heating process. Expansion vessels work at pressure. If this pressure is lost, the expansion vessel cannot do its job and the boiler will fail to start or will automatically shut down.

Cardew

Edvin_Paus wrote: »

Expansion vessels are found in most boilers, especially, and are needed to cope with the extra water created by expansion during the heating process. Expansion vessels work at pressure. If this pressure is lost, the expansion vessel cannot do its job and the boiler will fail to start or will automatically shut down.

That is understood by the OP. It is losing pressure because of a leak!