You must have a leak somewhere, or the system is overpressurising and venting off through the red valve and out through the overflow. The system is designed to vent off at 3 bar, 2.5 bar seems a little high to me, once the system gets going and hot it could easily creep up and vent of.. then when cool it drops right off again.
Fletch
December 2007
howtomendit.com for free repair help, information and advice.
