my preheat on my baxi combi instant 105e works fine ,but when i turn on the hot water tap the boiler won`t fire up.when i put cwntral heating on and the turn the hot tap on i do get hot water.the water pressure is fine.is the pcb at fault or is it something else?

darren, September 2006

sounds like ur diverter valve/microswitches

gas man, September 2006

Hi, sounds like the domestic hot water flow switch. as far as i can remember its a paddle switch so if you bridge it out the boiler should fire up. this is obviously only a quick check to prove the switch is faulty. also check for continuity accros the flow switch terminals. make sure you don't get mixed up with the heating flow switch. if your not sure get someone to recommend a good heating engineer.

Paul, September 2006