Central heating problems are not to be confused with boiler problems although they are closely related. This section deals with problems relating to cold radiators, radiators that are hot at the bottom and cold at the top and radiators that are cold at the bottom and hot at the top. This section also contains advice on what to do if you have one radiator that is not heating up at all.
Radiators cold at the top
Cold radiator at top If your radiators are warm at the bottom and cold at the top then they probably just need bleeding. Air can get trapped in the radiator, which rises to the top and prevents the hot circulating water from reaching the top of the radiator. To remedy this please see here- bleeding radiators
Radiators cold at the bottom
Radiators that are hot at the top and cold at the bottom can normally not be helped by bleeding as it normally means that the radiator is full of sludge. You can get professional power flushing carried out on your system, but it is expensive. You could always try a DIY powerflush
Radiators warm upstairs but cold downstairs
Cold downstairs radiators When central heating radiators are warm upstairs and cold downstairs it often means that there is a problem with the pump. You should check the pump is running and if it is not ensure that no fuses have blown etc. If the radiators have always been cold downstairs there is a chance that the radiators need balancing, but if all of a sudden the downstairs radiators are cold this points to a pump or circulation problem. To check for a blown fuse please see here- blown fuse testing If you are certain that the pump is at fault here are the instructions for replacing it- replacing a central heating pump
One cold radiator on a central heating system
If a radiator is completely cold this can be a couple of things. Firstly you need to ensure that the lockshield valve is open (Picture to left). You will need a spanner to check that the lockshield valve is open as the plastic cap on the top does not always operate the valve.
Another possible cause of a single cold radiator on a central heating system is a faulty thermostatic radiator valve (picture to left) To check this you need to remove the thermostatic head from the valve. You will then see a pin sticking up, if this pin is stuck down you have found the reason for the cold radiator. Spray the pin with a spray penetrant and try giving the valve body a gentle tap with a soft faced hammer, or try pulling the pin back up if you can grab it without damaging it. If you cannot get the pin to move you may have to drain down the system and replace the valve.
