One of the most asked questions we come across as plumbers is how to bleed radiators. It saves you time and money.

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Firstly, radiators only need to be bled of air when the top of the radiator is cold. If the bottom of the radiator is cold, it is likely to be a sludge problem. If you have a pressurised heating system, make a note of the current pressure so you can re-pressurise it after venting. Here’s how to bleed radiators.

1. Turn off the heating system so the pump is not running. This is just a precautionary measure because sometimes pumps can actually suck air into the system. Ensure the radiator valves are both open.

2. Find an old towel or rag and locate the bleed valve on the rad. Make sure you have the towel covering the wall and floor to prevent any spillage. Radiator water can be black and will stain walls and fabric so be careful. Using your radiator key (female square) turn slowly anticlockwise until you hear air hissing out. Wait until water comes out and close the bleed valve. All done!

Sometimes on pressurised systems you will need to top up the pressure as the air is released. Click here for information on re-pressurising sealed systems.

Often bleeding a radiator will not solve the problem. Sometimes air stops coming out even when you have pressure in the system or water in the feed and expansion. In these cases it is likely to be an air lock in the pipe work. Usually this requires backfilling the system or radiator removal and checking. Both should only be done by a competent heating engineer.