My boiler didn't always fire up even though the fan was on and and asking for heat. The piezo igniter didn't always work, especially when boiler was on and return water was not completely cool. This was on a Wickes heat60 boiler made by Halstead boilers

Teacher, December 2010

I found that the boiler would sometimes fire up when the circuit board was removed and the wires to the thermistor were wiggled, suggesting poor contact. So I removed the entire PCB after disconnecting all the connectors (take a digital picture first to remind you of what goes where), then use a hand lens or low power binocular microscope to view the soldered joints. I found over 10 dry joints which I re-soldered. It now works perfectly.

Teacher, December 2010