hot water tap not working in bathroom?

Hi Grant, you could be right, the water may well have frozen in the roofspace and if possible check it and see. Turn off the water to the roof if possible if this is the case to prevent a disaster while your out when it thaws (should a pipe have burst) Other possibilities: if there is no lid on the tank in the roof, a bird or something may have fallen in the tank and is now blocking the pipe inside it. OR - the ball valve has stuck in the tank and just needs knocking down to start it refilling. Try those options first if not it could be airlocked and need a small piece of hose pipe between hot and cold taps to force out the air in the system.
Good luck, hope you dont drown...

Bucket head.
December 2010