How to bleed your radiators

When to bleed them

• At the start of winter, before you put the heating on properly.
• When a radiator is cold at the top and warm at the bottom.
• When you hear gurgling or water running inside the radiators.

What you need

A cloth and a glass. And, if your bleed valve needs one, a radiator key: many open with a coin or a flat-head screwdriver.

Step by step

1. Turn off the heating and wait for the radiators to cool down. The water inside comes out very hot and can scald you.
2. Start with the radiator closest to the boiler and work towards the furthest one. If the house has two floors, do the ground floor first.
3. Put the cloth and the glass under the bleed valve, the small fitting at the top, at one end of the radiator. Open it slowly, a quarter of a turn: you'll hear the air coming out.
4. When only water comes out, with no air, close it. There's no need to tighten it hard.
5. When you've finished, check the boiler's pressure gauge. With the heating cold it usually reads between 1 and 1.5 bar. If it has dropped, that's normal: it needs topping up. We explain how on the error 108 page.

Then turn the heating on and check that all the radiators heat up from top to bottom.

If you have to bleed or top up often, the air or the water loss is coming from somewhere: book an engineer. And if the radiator is cold at the bottom, or still won't heat up after bleeding, bleeding won't fix it. If the bleed valve drips when you close it or won't open, don't force it.