Su, not familiar with Sime products but if yours is a combi and you're repressurising the central heating, then the pressure is dropping it sounds as if the dump valve is open (this is used to release pressure for maintainance) or you have a leak somewhere in the plumbing! See if you can find where the 'dump' drains to. With regards to the possible leak - pressurise the system and bleed air from all rads. Then listen for hissing. You may need assistance from someone to keep the system pressurised. Know how to dump pressure and drain the system down before doing this to safe potential flooding.
DH
April 2006
howtomendit.com for free repair help, information and advice.
