My Worcester Highflow 400 will not fire up, it has been tempramental for a while in going off on the thermostat on the boiler (no room thermo fitted) and not coming back on. The thermostat was replaced a week ago but now this morning it did not fire up at all. Went off last night but came back on after I switched if off at the power for a while.
Any ideas on the problem

John, January 2013