Pressure loss

You either have a leak in the system, or your radiators are corroding because you didn't put inhibitor in.

Christian.

See below.

Probably Ed Sirett's faq cover the answer, but I had a similar loss of pressure problem, and it turned out the air expansion vessel ( which has a rubber diaphragm in it ) had lost its integrity. The result was that there was no expansion space in the system, and when the CH water was heated, it expanded, elevated the system pressure too high ( as there was no expansion space ), and blew CH water out of the overpressure relief valve ( tripped at 2.4 bar ). I never saw it happen as I was ever outside to watch when this must have been happening.

The cure, if that really is your problem, is to recharge the expansion vessel via the top-up valve on it, and see if the problem recurrs ( may be necessary to wait a week or two if it's a slow leak ). If it does, the vessel diaphragm may be leaking and you'll need a new one.

Andy

A neat trick to use to find whether your expansion valve is blowing, is to but a balloon (or condom if inclined) over the valve outlet. Obviously, the balloon inflates with water or is blown off if the valve engages ;-)

Brad.

Yep .... you have a leak.

It may be so small that it is evaportaing off hot pipes soyou don't see it.

Rick

Look for staining. Also, catch the system when it's been off/cold for a while, and feel all the joints, valves, radiator plugs and bleed nipples, etc for any moisture.