Vaillant Thermocompact losing pressure

[rsk289]

Hi all - new here, and looking for ideas. My Vaillant Thermocompact VU 142 1E/282 1E was installed around 10 years ago, in a new build. During that time I've had to repressurise it 2-3 times, but since Christmas this has jumped to 3 times (in 2 months). I can't find any leaks anywhere in the house, or the boiler. I'm hoping desperately there's no leaks in the pipework, as the house is open-plan steel framed, with concrete beam-and-block first floor and full cover solid oak tongue-and-groove flooring over chipboard panels. Pipework is all plastic, once away from the boiler.
Is there a boiler fault that could cause this, or am I going to have to start attacking the floor?

 

[wards]

check prv HTH
si

 

[LIFES A GAS]

Watch the pressure gauge on the boiler after everything is up to temperature, If it rises to 3 bars then the pressure relief valve will open and release some pressure (water) via the pipe work to outside, probable cause if this is happening is the expansion vessel has lost air pressure, if so you will need to drain boiler and re-pressurise the expansion vessel.
Martin.

 

[rsk289]

Thanks, - BG are supposed to be coming on Monday (2nd time lucky) to check it. On the phone they didn't sound very confident of finding the problem, as it's taking 3-4 weeks to lose pressure. We'll see - this info is very useful as it gives me something to go on.

It never gets quite as high as 3 bar - should I pressurize it to 3 to test?

 

[LIFES A GAS]

No, the system pressure (water) should be at around 1.2 bar on most Vaillaints but check in the manual, the air pressure in the expansion vessel should be around 0.8 to 1.0 bar this has to be done before pressueising the system (water), is all is correct the gauge which displays the system pressure should not rise as the system heats up, if it does then the expansion vessel probably is the reason,
Hope this helps, Martin.