we recently had to have the thermo couple replaced in the boiler, the central system was off for around 24hrs and when we restarted the system we could not get the radiators to come on. after cosing them all off and opening them up in turn they evenually came on.the system went off at night but when the system restarted in the morning the pump was noisey ( whining ) with an occasional bang and there was also no heat at the radiators. I turned off the system for around an hour a turned it back on again, all seemed to be fine, in the evening the pump again became noisey followed by the radiators going off again. we are occasionally getting a bang from the boiler as well. Any ideas any one!!!