Finding that one of the radiators in your home is cold can be perplexing - especially if all your other radiators are functioning as normal, the boiler is on, the pump is working and the thermostat is set to demand heat.

Check flow and return pipes

If you find one of your radiators is not getting warm, check the connecting flow and return pipes. If they are cold, no heat is reaching the radiator.

Check the lock shield valve

Now check that the lock shield is open. Remove the lock shield cap, then use an adjustable spanner to turn the lock shield valve anti-clockwise as far as it will go. Now check the flow and return pipes to see if they are hot. If they are getting warm, you know the radiator is receiving hot water. The lockshield valve is the valve on the radiator that is usually covered by a plastic cap and is situated on either the bottom left or right of the radiator.  

Cold spots: is air trapped in your radiator?

However, you may find that your radiator is still not working as normal. Check to see if it is warming up. If you find that it is warm at the bottom but cold at the top, you have the symptoms of air being trapped.

The next step is to bleed the radiator. It's important to turn off the boiler and pump before you begin.

Read our guide on How to bleed a radiator.