Halstead High Ace Problem - Pressure related

[jonny00stars]

I have a Halstead High Ace which appears to be loosing water pressure. When switched off the boiler water pressure appears to fall to nil. I have then refilled the pressure and switched the boiler on again and it appears to work fine. However when it turns off after a timed program the after pressure slowly disappears and eventually falls to nil meaning I have to start the process of refilling again.

Any suggestions. This could be one for the professionals.

 

[gas4you]

Apart from the obviuos of checking for leaks on the system, see FAQ's on how to check the expansion vessel.

 

[MANDATE]

Looks like expansion vessel has lost its air pressure and there is nowhere for the hot water to expand to, so it does the next best thing and comes out from the pressure relief valve.
If you find the PRV outlet pipe (outside near boiler) and secure a plastic bag on the end, you'll see if it collects water.
Also once opened these PRVs rarely produce a good seal, so they still leak a little when the boiler is not in use.