Some boilers cut out for safety reasons.
If the pump fails then the water in the boiler becomes steam and a thermal cutout may trigger, you will usually hear the water boiling in this case.
possibly a faulty thermocouple, this device confirms that the pilot light is lit, if it thinks that the pilot light is out it will cut off the fuel supply.
May have a cut out if the flue is blocked.
gruff, March 2010
