Cold at the top: trapped air
If a radiator is warm at the bottom but cold at the top, air is trapped inside and stopping the hot water reaching the whole panel. Bleeding the radiator lets the air out and usually sorts it in minutes.
If you find yourself bleeding the same radiators again and again, air is getting in from somewhere — often a small leak or a failing part — and that’s worth having looked at.
Cold at the bottom: sludge
If a radiator is warm at the top but cold along the bottom, the likely cause is sludge — a build-up of rust and debris that settles and blocks the flow. Bleeding won’t help here. A power flush clears the system and gets everything circulating again, and it’s a job for an engineer.
One cold radiator, the rest fine
If a single radiator stays cold while the others heat up, check both valves are fully open. If they are, the system may simply need balancing — adjusting the flow so heat reaches every radiator evenly rather than favouring the ones nearest the boiler.
All radiators cold
If none of the radiators warm up but you have hot water, the fault usually sits with the circulation pump, a diverter or motorised valve, or the thermostat. These aren’t DIY fixes — they need testing and, usually, a part replaced by a Gas Safe engineer.
Radiators still cold after a bleed? If you’re in South Manchester or Cheshire, we’ll find out why — trapped air, sludge, a stuck valve or a failing pump — and get your heating working properly again.
See our boiler repair service
