Top of Radiator Cold and the Bottom Hot
This is usually a result of air in the radiator which has risen to the top and is stopping any more hot water filling the radiator.
It is cured by “bleeding” off the air from the top of the radiator by opening the bleed nipple (a small square peg at the top of the radiator, usually protected by a round cast in the radiator body) and allowing the air to hiss out.
Hold a cloth close to the bleed nipple and when water starts to come out the air should have gone.
If your radiators need constant bleeding then too much air is entering the system and the problem is a bigger one requiring a central heating engineer to have a look.
Top of Radiator Hot and the Bottom Cold
Rust and sludge has probably built up in the bottom of the radiator and this will displace any water leaving the bottom of the radiator cold. Have a look at our project on Draining Down the system and once drained down flush the radiators out.
Proprietary sludge removers can be used to clean systems through. Theses are on sale at all plumbers merchants but read the instructions before use.
Downstairs Radiators Hot and The Upstairs Cold
This generally means that the feed and expansion tank in your loft has run dry which can indicate a problem with the valve. This needs addressing quickly and a change of valve is usually in order.
This is not a huge job and, as long as you have turned off the water and is well within the capabilities of a DIY enthusiast.
Upstairs Radiators Hot and the Downstairs Cold
This possibly indicates a faulty central heating pump and this should be checked by a heating engineer.
No Radiators Getting Very Warm
This shows a build up of rust and sludge and the instructions above for draining down should be followed.
Radiators Warmer Nearer the Boiler
This shows your system needs balancing. This can be done by turning the valves down on the radiators nearest the boilers to restrict the flow to them and allow those furthest away a greater share of the hot water.
Go to our video section on central heating to watch a selection of videos relating to your heating system and solving potential problems and issues relating to your radiators.
If you are experiencing issues with your TRV's then see our TRV's (thermostatic radiator valves) project here.