I followed the fault diagnosis and replaced the flow switch. However the boiler reset kept tripping out (overheat thermostat). I replaced this and the heating is working perfectly but no hot water at all. When there is demand for hot water the boiler does nothing - like it hasn't detected it at all - the fan doesn't start, nothing! What's next? Could the new flow switch be faulty?

Rob, October 2008

Easy enough to check - use a multimeter and check for continuity through the two pink wires when a tap is running.

If switch is making, and boiler not responding, then board fault.

BunSlinger, October 2008