if you have a thermostatic radiator valve, it is probably sticking in the closed position. to correct this, remove the head and gently tap the pin which will be pretruding from the top of the valve. If you dont have trv's, you most probably have an air lock. turn off all of you other radiators, select heating only and it will force the hot water around the problematic radiator
gasmandave, December 2008
