If your hot water at your taps is getting hot, the circulating primary water must be getting hot also. Have you checked that the primary water pipes at the hot tank are good and hot? If they are, the boiler is stopping firing because all its thermostat can decide about is the water inside it, and that is reaching the 'stop' temperature. To see if this is so, turn up the thermostat on the boiler - if the boiler starts firing again, you should look at whether the valves which allow the primary water to go to the cylinder and to the radiators are behaving. It sounds as though the valve controlling the CH feed is not allowing enough flow to the radiators - or - that the HW valve is permanently wide open and that that flow is taking all the hot water from the boiler; a combination of the two may also be present.
ded, January 2005
