Radiators and Bleed Valves: Clearing Trapped Air
A cold patch at the top of a radiator with warmth below is almost always trapped air, cleared through the small bleed valve at the top corner.
A cold patch at the top of a radiator with warmth below is almost always trapped air, cleared through the small bleed valve at the top corner. It's one of the few heating faults most people can safely fix themselves, though repeated air suggests a cause worth investigating.
What it does
The bleed valve is a small screw-operated vent that lets trapped air escape from the top of the radiator, allowing water to fill the space it occupied.
How it fails
The valve itself rarely fails, but seized threads on old radiators can make it difficult to open, or a worn washer lets it weep afterwards.
Repair or replace
Bleeding is simply done with a radiator key; a valve that won't seal afterwards or is seized solid is replaced rather than forced.
Questions we get asked
Can I bleed a radiator myself?
Yes, this is a straightforward job for most people with a standard radiator key and a cloth to catch the water.
Why does my system need bleeding so often?
Frequent air usually points to a slow leak somewhere letting air in, a failing pump drawing air in, or an automatic air vent that's stuck.
Is changing a radiator valve notifiable gas work?
No, bleeding radiators and replacing a bleed valve is plumbing work, not gas work.