boiler looses pressure when heating not on ,but no leaks?

This is more likely to be a perforated diaphram on the expansion vessel.If the pressure goes up rapidly when the heating is on that is the most likly cause.

Sig Lofnes
November 2006

Had a friend with this kind of problem, and it turned out to be the expansion vessel had no pressure in it. Get yourself a car tyre pump and put in some air, maybe 6 pumps, and see how you go. The expansion vessel should have a car tyre type valve in it.

Dode
December 2005