One Radiator Not Working

Stuck or closed TRV (thermostatic radiator valve)

The most common cause. TRV heads can seize in the closed position, particularly if left at zero ('anti-frost') during summer. Remove the head and try pushing the pin down — if it springs back, the valve is working.

Sludge blocking the radiator

Magnetite and corrosion debris settles in the bottom of radiators, blocking flow. A single radiator colder at the bottom than the top is a classic sign.

Air lock in the radiator

Air trapped in the radiator prevents hot water entering. Bleed the radiator — hot water and air should escape through the bleed valve.

Closed lockshield valve

The non-adjustable lockshield valve on the return side of the radiator may have been closed during a previous repair and not reopened. Open it 1.5–2 turns anticlockwise.

Isolation valve closed after previous work

If the radiator was isolated for decorating and the valve not fully reopened, it won't heat. Check both valves are fully open.

Why is one radiator cold when all the others work?

Most commonly a stuck TRV, an air lock, or a radiator blocked with sludge. All three are quick to diagnose and fix — often in a single visit without touching the boiler.

Can I fix a cold radiator myself?

Yes, for some causes. Try: 1) bleed the radiator, 2) check TRV head pin is free (press it — it should spring back), 3) check lockshield valve is open. If none of these work, call an engineer.

My radiator is warm but not hot — is that normal?

It depends on your TRV setting and room temperature. If the TRV is set to 3–4 and the room is at 20°C, the valve should be partially or fully open. If the radiator feels lukewarm even when the TRV pin is free, there may be a flow issue.

How much does it cost to fix a cold radiator?

A standard single-radiator visit starts from £150+VAT. We'll diagnose and fix the issue within the same visit in the vast majority of cases.