A little while ago (around Easter) I posted a thread on here asking for help with a de pressuring boiler, which htg_engineer pointed to the expansion vessel. From then till the time the heating was turned off for summer it worked fine.
A few weeks ago the boiler has been de pressurising again - this time with no heating on and only hot water (the boiler is a Ferroli Combi boiler by the way). Doing a test cycle of the heating the pressure has again gone up to nearly 3 (when I switched it off).
I commented at the time that the bathroom radiator developed a small leak near the bleed point. I'm assuming that because water can get out here, air can get in and cause pressure problems with the expansion vessel. I've now got a chrome towel rail which I'm installing tomorrow in lieu of this rusty radiator. Obviously this will mean draining the system manually so it'll be a good time to pressurise back to 1bar!
My thoughts are what caused the vessel to lose pressure when the heating wasn't on for nearly 6 months, and can any other factor cause problems? I don't want to replace anything else in case there was nothing wrong with it (a towel rail I'm happy with - another new radiator not so!).
Thanks for your help in advance!