Another pressure problem

[wozza56]

Right i have a Grant combi 90 mk11 and it seems to have a pressure problem,when the heating is on its all lovely jubbly and the pressure stays at just over 1 bar but as soon as the heating goes off the pressure drops to zero until the heating starts again ,i have brought the pressure up manually via the valve but then when the heating starts it gets too much pressure about 2.5 bar so i have to bleed a rad to bring it back down
So has anyone got any ideas how to sort it out?

 

[wozza56]

Anyone ?????????? please i dont want to damage the boiler

 

[Burnerman]

Check out the FAQ's regarding repressurising the expansion vessel, Woz
John

 

[miajanjua]

I agree, you need to re-pressurise the EV to 1 bar