central heating

[ploppy]

why should one radiator stay cold,when all the rest get hot.

[trendypaul]

Assuming the valves are turned on (I'm sure you have checked this, if not turn both valves anti-clockwise until they stop) it could be that it is full of air and needs bleeding.  There is a valve at the top of the radiator that if you loosen will release any trapped air.  Take care when opening as the water will move up the radiator and spray out when it gets to the top.  The other problem could be that hte radiator is blocked with debris and needs flushing.  If you are confident you could do it yourself.  The radiator needs to be removed (after turning both valves off) then flush it out by putting water through it with a hose.  If you have any doubts about your skills you should get a plumber in to sort it as you don't want to flood your house with dirty central heating water.

[cyprus1]

There's probably air in the system. Try venting the highest radiator on the system

[landie]

As previous answer except that you should bleed when the circulatory pump is off.