Radiator Not Heating: 5 Fixes You Can Do at Home
Independent guide — no official affiliation with the platforms mentioned.
Short answer
If part of a radiator stays cold, the most common cause is trapped air at the top: bleed it with the bleed key. A single cold radiator often has a closed or stuck thermostatic valve; a cold bottom with a hot top means sludge and needs a system flush. With pressure below 1 bar, refill the boiler first.
01 — Step-by-step fix
Step-by-step fix
Check the boiler pressure
Below 1 bar circulation weakens and the furthest radiators stay cold. Refill to 1.2–1.8 bar with the filling loop. This alone fixes many 'radiator not heating' complaints.
Bleed the radiators
Hot pipes with a cold top means trapped air. Open the bleed valve slowly; wait for the hissing to stop, close when water appears. Work through all radiators from the top floor down.
Put a towel under the bleed valve and top up the boiler pressure after bleeding.
Check the thermostatic valve
If the TRV is closed or stayed closed all summer, its pin can stick. Turn it to maximum; if needed, remove the head and gently free the pin.
Cold bottom = sludge
Hot top and cold bottom indicates sludge. Partial drain/flush can help temporarily; the lasting fix is a power flush and/or a magnetic filter — hire a heating engineer for this.
One radiator or many? Diagnose
Only one cold radiator: that circuit's valve or radiator. Several (especially the furthest): pressure/air/circulation speed. None heating: boiler mode, heating water temperature or external thermostat.
Tips
- Bleeding every radiator at season start prevents most winter complaints.
- Turning the pump to speed '2' helps far radiators in large homes.
- A room thermostat in direct sun makes the boiler stop early — relocate it.
02 — Frequently asked questions
Frequently asked questions
How often should I bleed radiators?
Once per season, at the start of heating. Repeat after adding water to the system or whenever cold spots return.
I bled it but it's still cold
Confirm the TRV is open, boiler pressure is above 1.2 bar and the room thermostat (if any) is in heating mode. If all are fine, that circuit's valve may be faulty.
How do I recognize sludge?
Hot flow pipe but a cold body, orange/brown water when draining, and patchy heat patterns across the radiator.
Links in this guide point to official platform pages. Steps may change with platform updates; check the page date.
03 — Related guides