One radiator is cold
- Cold at the top, warm at the bottom: trapped air. Bleed the radiator.
- Cold all over: check both valves are open. The thermostatic valve (the numbered dial) may be turned down, or its pin may be stuck. Take the head off and gently tap the pin. It should spring up and down. If it doesn't, an engineer can free or replace it.
- Cold at the bottom, warm at the top: usually sludge collecting inside. This needs an engineer, and may mean cleaning the system.
Some radiators are cold, usually upstairs or furthest from the boiler
The system may need balancing, so the hot water reaches every radiator evenly instead of taking the easiest route. An engineer can do this, or you can if you're confident, by partly closing the valves on the radiators that heat up fastest. Low pressure can also cause this. Check your pressure.
All the radiators are cold
- Check the heating is switched on at the boiler and the programmer, and turn up the room thermostat.
- Check the boiler pressure and look for a fault code on the display.
- If the boiler is running but nothing warms up, the pump or a valve may have failed. That's a job for an engineer.
Never take the casing off your boiler or try to repair gas parts yourself. That work must be done by a Gas Safe registered engineer. With boiler cover, your provider sends one for you. Compare boiler cover.
Radiators are usually only covered by boiler and central heating plans, not boiler-only plans, and sludge is often excluded. What boiler cover doesn't include.
Have boiler cover?
Call your provider before paying an engineer yourself. A repair like this is exactly what cover is for.
No cover yet? A new plan won't pay for a fault you already have, because problems that exist when you join aren't covered and there's a waiting period at the start. It can protect you next time.
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Last updated 30 October 2026