Thanks Blasphemous - I think you've got it spot on!
I put 0.5 bar back into the system and then watched the blow-off pipe on the outside wall, a constant dripping every couple of seconds came from it (and is still coming it from some hours later).
I'll get an engineer out to look at it in...
Came back from holiday to find my boiler (Sime Friendly Format 80E) with 0 pressure. Hot water still works and when I try to repressurise the system (using single valve on filling loop) some radiators become very warm (some don't) but the pressure will drop from 1 bar to 0 in less than an hour...
Came back from holiday to find my boiler with 0 pressure. Hot water still works and when I try to repressurise the system some radiators become very warm (some don't) but the pressure will drop from 1 bar to 0 in less than an hour. There are no obvious leaks.
Before I went on holiday system...