C/H sealed system pressure question

[efiste2]

Central heating system is a Y plan I think (3 way motor valve)....with a worcester 24i boiler (not combi). When cold the pressure guage is at zero, but when operating the pressure is in the green range on the dial......but falls back when totally cold again,
I have topped up the system a couple of times, and the same happens, all radiators are bled and there are no obvious signs of a leak anywhere......but Im in no way a plumber/boiler tech

 

[petit_pablo]

Likely flat expansion vessel and a dripping pressure relief valve.

Check outside for a dripping open ended pipe near where boiler is situated.

See the FAQs on how to recharge and expansion vessel.

 

[denso13]

http://www.diynot.com/wiki/plumbing:faq:faq7

 

[efiste2]

its been like this for a while, will any damage have occured.......system works fine at the moment.....

 

[petit_pablo]

Not majorly, pressure relief valve will probably need replacing though