We bought this house 6mths ago. Didn't use the heating till autumn. Turned it on and found a small leak in one of the pipes right at the boiler. Turned it off, made an appt with a corgi reg engineer. He came, switched it on and there was no leak. For his fee, he bled all my heaters for me! He topped up the system pressure, left it on for half an hour then left me to it. That was ten weeks ago, it's been fine since.
Yesterday, we had the heating on and noticed the pressure had dropped and a few rads had air in. We bled them, topped up the system pressure, and when we put the ch on again, the pressure dropped again. There is no problem with the hot water, no system noises. Our boiler is a worcester 24i junior, there is no water tank. Most of the rads have trvs. There is no noticeable leak any where obvious, including where it was before. Our outlet pipe thingy for excess water (that is used for pressure relief) was blocked before but the guy fixed it. I have not yet checked if it is dripping.
Problems: the boiler has been boxed in by the wall, and I can't get it open - neither could he. The pressure relief button or whatever is incredibly hard to reach for this reason. I live in a flat and don't want to flood my neighbours at this time of year by messing about with it, and we cannot locate a stopcock anywhere on the property (have checked neighbours' flats and ours is not where theirs is - last owner fancied himself as a handyman.) and the engineer I already called out had no idea what caused the problem. I don't really fancy paying another huge sum to have a different guy come out and tell me he can't do anything, or start pulling stuff up before Christmas...
Has anyone got any ideas what I can do to try to get it sorted? The pressure has dropped completely over ten weeks, then by 0.5 bar over about 4hrs yesterday...is this likely to be a big leak somewhere, or venting to outside?
I don't even know what the right questions are to ask, so any wisdom would be much appreciated!