A single cold radiator when the rest of the house is warm is almost always one of four things, and where the radiator is cold tells you which.

Cold at the top, warm at the bottom

Air. Hot water rises, air collects at the top and stops the radiator filling. Bleed it and check the boiler pressure afterwards, because bleeding drops it.

Cold at the bottom, warm at the top

Sludge. Corrosion settles in the bottom of the radiator and blocks the flow. Bleeding will not shift it and it gets worse over time.

This normally needs a power flush, which cleans the whole system rather than one radiator.

Cold all over, while others are fine

Usually a valve. Check the thermostatic valve is open, and check the lockshield valve at the other end has not been closed. On a system that has been balanced badly, one radiator can be starved while the rest run hot.

Cold downstairs but fine upstairs, or the reverse

That is a system-wide issue rather than one radiator: often the pump, a zone valve that has failed, or a system that has never been balanced. It needs an engineer.

All the radiators are cold

Then it is not the radiators. Check the boiler is firing, the pressure is 1 to 1.5 bar, and the thermostat and programmer are calling for heat. See boiler not firing up.

How Vantage can help

We cover Hertfordshire, Bedfordshire and Cambridgeshire and we carry out power flushing and system balancing as well as repairs.

Frequently asked questions

Why is my radiator cold at the bottom?

Sludge. Bleeding will not fix it and it needs flushing.

Should I bleed a radiator that is cold at the bottom?

It will not help. Cold at the top is air, cold at the bottom is sludge.

What is a lockshield valve?

The valve at the opposite end to the thermostatic one, used to balance flow between radiators.

Why do radiators stop working after summer?

Thermostatic valve pins seize when they have been closed for months. Freeing the pin usually fixes it.

Want it sorted properly?

If the fault keeps returning after a reset, it is telling you something is degrading rather than broken. Call 01462 506374 and we will diagnose it properly rather than swapping parts and hoping. Gas Safe registered 956889, 2 years on our own labour.