How to Bleed a Radiator: A 5 Minute Fix for Cold Spots
If your radiator is warm at the bottom but cold at the top, it has trapped air inside that is stopping hot water from circulating properly. Bleeding the radiator releases that air and usually fixes the problem in about 5 minutes.
What you need
- A radiator key (available from any hardware shop for about £1, or many modern radiators can be bled with a flat head screwdriver)
- A cloth or small towel
- A small container to catch any water
Step by step
- Turn off your heating and wait for the radiators to cool down. Bleeding a hot radiator means dealing with hot water, which is not pleasant
- Find the bleed valve. It is a small square fitting at the top corner of the radiator, usually on the opposite side to the TRV (the valve with the numbered dial)
- Place your cloth and container underneath the valve to catch any drips
- Insert the radiator key and turn it anticlockwise, about a quarter turn. You will hear a hissing sound as air escapes
- Keep the key in place and wait. The hissing will continue for a few seconds to a couple of minutes depending on how much air is trapped
- When water starts to dribble out (it will be dark, possibly dirty water), close the valve by turning clockwise. Do not over tighten
- Check your boiler pressure. Bleeding drops system pressure, so you may need to repressurise using the filling loop. Top up to 1.2 bar
Which radiators to bleed
If multiple radiators have cold spots, start with the radiator furthest from the boiler and work your way back towards it. This ensures air is pushed out of the system in the right direction.
If bleeding does not fix it
If your radiator is cold at the bottom but warm at the top, that is a different problem. Cold at the bottom means sludge (iron oxide and rust particles) has settled in the bottom of the radiator, blocking water flow. Bleeding will not fix this. The radiator needs flushing or the whole system needs a powerflush.
Need help with your boiler? Our Gas Safe registered engineers cover the North East. Get in touch today or call 07579 760536.