Hello I am new here and would like some help ... have a 'Brittany 80' Combo Boiler . When I turn on the hot tap all is OK for about a minuite ( although the water is only luke warm ), then the 'BAR' Pressure increases to the point where the pressure releaf valve blows !!! ... It is driving me nuts as the CH is working fine. Please help. Thank you
It could be a few things, you say the CH is working fine but does the pressure gauge rise ? If not is the temperature set quite low, turn the thermostat up and see what happens as the DHW will be at a higher gas rate.
It could be the expansion vessel, the gas pressures could be set too high, or mains cold water is finding it's way to the sealed system either a pinhole in the plate heat-ex or as rosebery says the diverter, however if the mains cold water supply pressure is greater than what the boiler pressure gauge sits at when off - then you can rule this out.
Thank you both very much for your answers.
I was thinking that the diverter vaulve was the problem ( stuck on Heating only ) ... ie ... just giving extra hot/boiling water to the rads when DHW is turned on,,, and only luke warm from the tap ... Am I right in thinking this ?