Why is my radiator cold at the top?

A radiator that is warm at the bottom but cold at the top commonly contains trapped air. Vaillant and Worcester Bosch both identify that temperature pattern as a sign that bleeding may be needed.

Bleeding is water-side maintenance, not gas work, but do it only with the heating switched off and the radiator cool. Use the correct radiator key, protect the wall and floor, open the vent slowly and close it when air has stopped and water begins to appear. Never remove the vent fitting.

Afterwards, follow the heating appliance's user instructions to check the system indication. If pressure has fallen, use only the user procedure for that specific model or call its installer. Do not remove a gas-boiler casing, adjust gas valves or improvise around boiler pipework.

If air returns repeatedly, the valve leaks, or the radiator remains cold, stop repeating the bleed and ask a heating professional to diagnose the system. Cold at the bottom is a different pattern and can indicate debris or poor circulation rather than trapped air.

Check the pattern only when the heating has had time to warm the system, taking care around hot surfaces. Compare several radiators: one cool top suggests a local air pocket, while widespread poor heating may have another cause. Repeated trapped air can indicate a system fault that bleeding does not repair. Keep a cloth below the vent and stop if the key does not fit, the valve is painted over, water will not stop or the fitting itself begins to move.

Sources

• How to bleed a radiator — Vaillant, accessed 14 November 2026.
• Radiator fact sheet — Worcester Bosch, accessed 14 November 2026.
• Gas safety: who can do the work? — HSE, accessed 14 November 2026.

On Leatmere

Use radiator bleeding and balancing and see radiator bleed valve.