Bleed your radiators before the cold sets in
A radiator that is cold at the top is full of air, not water. Ten minutes with a bleed key gets the whole panel hot again and stops your boiler running longer than it needs to.
Put your hand on each radiator when the heating has been on for half an hour. If the bottom is hot and the top is cool, there is air trapped inside. The boiler is heating water that never reaches the top of the panel, so the room takes longer to warm up and the boiler runs for longer to get there.
Bleeding a radiator lets that air out. It takes a few minutes and costs nothing.
What you need
- A radiator bleed key. Most hardware shops sell them for a pound or two, and some radiators have a screw slot that takes a flat screwdriver instead.
- An old cloth or a small jug to catch the drips.
How to do it
- Turn the heating off and give the radiators twenty minutes to cool. Bleeding a hot system can spray very hot water.
- Find the bleed valve. It is a small square nut inside a round fitting, usually at one top corner of the radiator.
- Hold the cloth under the valve and turn the key slowly anticlockwise, about a quarter turn. You will hear air hiss out.
- When water starts to dribble steadily instead of spitting, close the valve. Do not overtighten.
- Move on to the next radiator. Start with the ones on the ground floor and finish upstairs, because air collects at the highest points.
Check the pressure afterwards
If your boiler has a pressure gauge, look at it once you have finished. Letting air out lowers the pressure a little. Most systems should sit between 1 and 1.5 bar when cold. If it has dropped below 1, top it up using the filling loop under the boiler, or ask your heating engineer to show you how at the next service.
When to do it
Once a year in early autumn is enough for most homes. If you find yourself bleeding the same radiator every few weeks, air is getting into the system somewhere, and that is worth mentioning to your engineer.