I bought a new 4 bed detached house from Gladedale builders about 6 months ago. It has a Potterton Promax HE Plus boiler.
Since we moved in, the boiler pressure has always dropped.
It is set to 1.5 bar but within 1 or 2 days it drops to 1 bar, then 3 or 4 days later it drops to 0.5 bar then it slowly reduces towards 0 but never seems to get there. After 2/3 weeks I top it up to 1.5 bar.
To top it up from 0 to 1.5 bar is about `half a pint of water` according to the Engineer who came round.
Initially they said it was air in the system and they bled the rads but it didn`t solve the problem. Now they have resorted to shrugging their shoulders and saying they will have to monitor it.
There are no visible leaks anywhere but somehow its losing pressure.
Other than that it seems to be operating perfectly normally.
The pressure relief/safety valve, is there to discharge water from the system if the pressure gets too high, this is normally discharged to outside via a 15mm copper pipe or sometimes using the old tank overflow.
Check around the boiler for a 15mm copper pipe going through the wall to outside, then check this for leaks, some people put a balloon on the end to catch any water - and it wont affect the boiler as if it discharges the balloon will either come off the pipe or burst.
there is no pipe coming from the boiler but I think somehow it is linked to a plastic pipe with a plastic cap that is situated (literally) on the other side of the house at floor level. I recall them saying when we moved in that if there was too much pressure in the system then the cap would blow off to release the excess water and pressure.
Only thing is that this is positioned about 30 feet away from the boiler which is an awful long way for water to travel!!??
I intend to have a good look at this tonight. thanks again