Why are my radiators cold at the top or bottom?
Updated 7 November 2026
Where a radiator is cold tells you a lot about what's wrong.
Cold at the top, warm at the bottom
This almost always means trapped air. Bleeding the radiator fixes it.
- Turn the heating off and let the radiators cool.
- Put a cloth under the bleed valve at the top corner of the radiator.
- Use a radiator key to turn the valve a quarter turn anticlockwise. You'll hear air hiss out.
- Close it as soon as water starts to appear.
- Check the boiler pressure afterwards and top it up if it's dropped below 1 bar.
Cold at the bottom, warm at the top
This usually means sludge (rust and debris) has settled in the radiator. It won't fix itself. An engineer can flush out the radiator, or power flush the whole system, and fit a magnetic filter to stop it coming back.
One radiator completely cold
Check the valves at both ends are open. If it's a thermostatic valve, the pin underneath the head may be stuck. Taking the head off and gently tapping the pin often frees it.
All radiators cold
If none of them heat up, the problem is likely the boiler, the pump or the controls. Run through our boiler not working checklist first. If the boiler fires but the heat never reaches the radiators, it's usually a central heating repair, such as a pump or valve.
Need it sorted? Central heating repair in Newcastle typically costs £150 to £600. A local engineer will give you a price before starting.