I've got a problem with my combi boiler, ive recently had a rad off to decorate and now its all back on i cant get hot water. The pre heat function works correctly but as soon as i open a DHW tap the flame light goes out and the hot water goes luke warm then cold. Ive followed the standard stuff like checking the diaphram in the DHW differential valve and checked continuity through the microswitch all seems ok, I know its all pointing to the PCB but i was hoping someone might have a less expensive alternative to try. PS the CH is working well all air out of system etc, and pressure is holding at 1.5 bar, If you can help i will be very grateful. Cheers.

ye, ive done everything i can. Ive done the fault finding in the installation manual and stop at pcb everytime, its like the boiler isnt sensing the dhw is flowing but it must be coz the neon flashes just the boiler doesnt light but if ch is on, the burner goes out. I just cant get my head round why its started playing up when it was fine before. Thanks for your reply by the way, if you can suggest trying anything else let me know, Cheers. After thought, is there some kind of thermo switch that cuts burner off when the water is hot enough and could it be stuck/knackered so the water doesnt heat up coz switch is open/closed.

I dont think so, is it worth me havin' a look in case its air locked? The ch is working so i thought it couldnt be and i do get some DHW but only whats in the preheat.