have had the powermax 155x for 7 years now and its given us no grief, up to now. with the cold weather on its way i thought i'd check that the central heating is working. turned the thermostat up and waited to hear the pump start and the boiler fire up. nothing happened. turned on a hot water tap and the boiler started up and fired. i've checked the thermostat and all seems ok there. anyone any ideas, pump maybe ???