BoilerTroubleshooting2026-02-26
Radiators Not Heating Up: What to Check
Cold radiators can mean trapped air, sludge, a stuck valve or a circulation fault.
When radiators stay cold while the boiler runs, the cause is usually air, sludge or a valve.
Air and sludge
Cold tops mean trapped air (bleed them); cold bottoms mean sludge needing a power flush. Both block proper circulation.
Valves and pump
A stuck thermostatic radiator valve or a failing circulation pump can also stop hot water reaching radiators.
Key takeaways
- Cold top = bleed trapped air
- Cold bottom = sludge, needs flushing
- Check radiator valves are open
- A weak pump needs service
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