my vaillant boiler model VC GB 242 EH is installed as a pressurised central heating & hot water system.

The pressure was set to 1.4 Bar when last serviced.
Suddenly, water is coming out at the overflow outside.
The pressure then dropped to 0.2 approximately.
When topped to 1.4 bar again, the same story repeats.

I suspect the internal Expanson Vessel. Do you agree?
If you do agree, if you have a picture to show where the repressurising valve is located, I would be grateful.

There are no leaks visible inside the house anywhere.

At this low pressure the CH is working as before! But the fault whatever it is must be rectified.

Thanks

Amal Roy
Peterborough

Mr Amal Roy, October 2009

Is the pressure relief valve (PRV) itself faulty? It is not hard to fit and replacements are available from uk-plumbing.com, or try a Google search for "190721 Vaillant"

cooliosbook, October 2009

Sounds like the expansion vessel or the pressure release valve is caput

Solar Man, October 2009

The pressure release valve should let go at 3 bar so I'd be replacing that first...consider the expansion vessel if the pressure fluctuates widely when the heating is on.

John, October 2009