How to Bleed a Radiator

Step 1
Fully open any thermostatic radiator valves, including heated towel rails, and run your central heating for ten minutes. Turn off the system. Put the radiator key into the valve in one of the top corners of the first radiator and slowley turn anti-clockwise. Have a cloth handy to catch any drips.

Step 2
If air is trapped in the radiator, it will escape through the valve and there will be a hissing sound as the air comes out. As soon as water begins to drip out, close the valve again and wipe away any water.

Step 3
Work your way around your system, repeating for each radiator. Take care not to open the valves more than necessary. Often air pockets will only occur in one or two of the radiators. Turn the heating on and check there are no dripping valves. Tighten if necessary.

Tips & Advice
- Cold spots at the bottom of the radiator are a sign of rust and sludge build-up that's sitting in the bottom of the radiator. Often this chemical reaction will produce a gas that will cause larger cold spots. The radiators will need to be flushed by a heating engineer.
- Make sure you know where the stopcock is located so you can turn off the cold water supply quickly in an emergency. Check the valve opens and closes easily.
- Don't leave the house empty and unheated for long periods in the winter, drain the central heating system.
- Bleed radiators at least once a year to release any air trapped in the system.
- Keep the names of a couple of local qualified plumbers on the kitchen noticeboard.
- Some systems have an automatic air release valve fitted. This usually has a small red top which should be slack to enable the air to escape.
- If your radiators are cooler in one area of the house, the radiators aren't properly balanced. The nearest radiators to the boiler are taking more than their share of the hot water from the system. Call in a professional to fix it.