This guide covers your radiators. For help with your heat source, see the Gas Boiler or Heat Pump pages.
How to Bleed a Radiator
When to do this: A radiator that's warm at the bottom but cold at the top has trapped air preventing hot water from filling it fully.
What you'll need:
- A radiator bleed key (available from DIY stores for around £2)
- A cloth or old towel
Steps:
- Turn the heating on to identify which radiators aren't heating correctly as there may be more than one.
- Turn the heating off and allow the radiators to cool completely before you start. This prevents scalding.
- Locate the bleed valve a small metal square or screw inside a round nut, usually at the top corner of the radiator.
- Open the valve by placing your cloth underneath it, then fitting the bleed key and turning it slowly anti-clockwise (a quarter to half turn is usually enough). You'll hear a hissing sound as trapped air escapes.
- Close the valve as soon as the hissing stops and water begins to dribble out steadily. Turn the key clockwise to close. Don't overtighten.
- If you have a gas boiler, check the pressure after bleeding, as it may have dropped. You can find a guide on how to do that by CLICKING HERE.
One Radiator is Completely Cold
If a single radiator is cold all over while the rest are working normally, follow these steps:
First, check the TRV setting. The Thermostatic Radiator Valve (TRV) is the valve with numbers (usually 1–5) that controls the temperature of that radiator. If it's set to 0 or the frost symbol, turn it to the highest setting and see if the radiator heats up next time the heating comes on.
If the problem continues, the TRV pin might be stuck in the closed position, preventing water from entering the radiator.
To free a stuck TRV pin:
- Turn the TRV head to its highest setting.
- Unscrew the knurled ring at the base of the TRV head by hand and lift the head off.
- You'll see a small metal pin on the valve body. If it's stuck down, that's the problem.
- Grip the pin gently with pliers and work it up and down a few times until it moves freely and springs back up.
- Refit the TRV head and set it to your desired temperature. The radiator should now heat up normally.
