I have a problem with my Potterton 80e gas boiler. Basically the ignition stopped about a week ago (have been using water heating element). Once I found and pressed the reset, the ignition started and the flame burned for abou 30 seconds before going out. This now seems to repeat, I can get it ignited every time after resetting but will only burn for a short time (and yes the controller is on and thermostat / water cylinder thermo up high). I am hoping this is not the PCB as this cost me 240 quid to replace last time? Anyway of fault finding with limited experience and no instruction booklet?