Four year old boiler, gauge playing up. shows very low pressure ie one or below one when CH is off. When on then the needle gradually rises up and goes beyond the green bar to almost red. I have on two occasions pumped up the pressure thinking it was too low only to find it going outside the green bar when the heating comes on.

Amar, December 2009

the problem you are describing is plainly one of expansion,when the boiler is cold the gauge will fall and when hot it will rise but should not rise too high if the expansion vessel is the right size for the property.check pressure of orange vessel with a tyre gauge if lower than 10 pounds then pump up with a bycicle pump and release excess water pressure by bleeding a rad,this boiler will always fail to safe and if the pressure becomes too high it will jettison the excess to the outside of the property

steve baxi, December 2009

Has the boiler been serviced? A registered gas safe engineer will be able to sort out your fault at the time of service.

RR, December 2009