your boiler has a low pressure switch which stops the boiler working when it loses pressure, what usually happens is that when you refill the boiler you push some dirt from your system into the switch which stops the water pressure from pushing the diaphragm inside it, which makes the switch, try to locate the low pressure switch in your manual and tap it to dislodge the dirt, you may be unlucky and need to drain boiler, remove the switch to clean it out
pauly, May 2010
