MY COMBI BOILER SOMETIMES LOOSES PRESSURE. WHEN I TOP MY SYSTEM UP TO 1.5 BAR, EVERYTHING IS FINE FOR A DAY OR TWO. THEN, THE PRESSURE GOES UP T 3.5 - 4 BAR AND STARTS VENTING AT THE OVER FLOW. I THEN BLEED THE SYSTEM BACK TO 1.5 BAR AND THE CYCLE WILL START AGAIN. ANY IDEA'S

GARY B, November 2008

Youwill need to change expansion vessel on boiler or
add another one into pipework if not possible to get at one onboiler.

plumbmend, November 2008

The expansion vessel has lost pressure or is knackered.Get an RGI in.

Gasman, November 2008