This guide is about your radiators. You might also need to consider your heat source. See below for additional information on gas boilers and heat pumps.
How to bleed a radiator.
When to do this: If a radiator is warm at the bottom but cold at the top. This indicates trapped air is preventing hot water from filling the entire radiator.
What you'll need:
- A radiator bleed key (These cost about £2 from DIY stores.)
- A cloth or old towel
Step-by-Step Instructions:
- Turn the heating on: First, switch on your central heating to identify which radiators are not heating up correctly. There might be more than one, so this step is vital to identify which radiators are not working properly.Â
- Turn the heating off: Once you've found the problem radiators, turn your entire central heating system off and wait for the radiators to cool down completely. This is a crucial safety step to prevent scalding.
- Locate the bleed valve: This is a small metal square or screw inside a round nut, usually found at the top corner of the radiator.
- Open the valve: Place your cloth under the valve to catch any water. Fit the radiator key onto the square and turn it slowly anti-clockwise (usually a quarter or half turn is enough). You will hear a hissing sound as the trapped air escapes.
- Close the valve: As soon as the hissing stops and a steady stream of water starts to dribble out, turn the key clockwise to close the valve. Be careful not to overtighten it.
- Check boiler pressure: After bleeding one or more radiators, you should check your boiler's pressure (see HERE) as it may have dropped.
One radiator is cold all over, but the other radiators are working.
- The first thing to check is that the Thermostatic Radiator Valve (TRV) isn't in the off position. The TRV is the valve with numbers on it (usually 1-5) that controls the temperature of that specific radiator. If this is set to 0 or a frost symbol, try twisting it to the highest number and see if things improve when the central heating system is next active.Â
- If the problem persists: The most likely cause is that the Thermostatic Radiator Valve (TRV) is stuck in the 'off' position.
- Solution: Free the stuck pin.
- Turn the TRV head to the highest setting (e.g., number 5).
- Unscrew the knurled ring at the base of the plastic TRV head. You should be able to do this by hand. Lift the head off the valve body.
- You will see a small metal pin sticking up from the valve body. If this pin is stuck down, it's stopping water from entering the radiator.
- Grip the pin gently with a pair of pliers and carefully pull it up and down a few times to free it. It should spring back up and move freely.
- Screw the plastic TRV head back on and set it to the desired temperature. The radiator should now start to heat up.
