When Central heating turned on from cold my system has an initial hi press surge (1-3.5bar), after header temp reaches thermostat cut out temp, the press falls back to 2bar over a few hours. The system psv/tsv lifts on occasion thus reducing cold stanby press to .5bar or lo system lock out press.

Have fitted new pump / thermostat. Any ideas?

Steve J., February 2005

sounds like your expansion tank at back of boiler need re-pumping up to 1 bar. you can do this with a foot pump. there is a valve on the tank, the cental heating system pressure has to be at zero. so you only measure the pressure within the tank. to do this turn the red three bar pressure relief valve anti clockwise.

Ryan, February 2005