good god!! not the boiler you want!

well the only knobs on the front are the thermostats for heating and water so they ant going to help getting the boiler working.

there could be a loose connection on the pcb as this is directly behind the knobs you are talking about. wouldnt advise going in there unless you know what you are doing?

as said by others, it could be the diverter valve but by moving thermostats on the outside of the boiler it will not fire up - so doubt it is this.


best bet so far would be the loose connection on the pcb