One Radiator Not Heating but Others Are Hot UK

Your heating’s on, most radiators are hot, but one stays stubbornly cold — a very common UK problem.

One radiator completely cold while all others heat normally

Is this your problem?

What to do

1. Go to the cold radiator.
2. Check both valves at the bottom are fully open (turn anti-clockwise).
3. If one valve is closed or only partly open, open it fully and wait 10–15 minutes.
4. If it warms up, the issue was simply a shut or stuck valve.

Safe DIY. No tools needed.

Stop and call a professional only if the valve won’t turn at all.

Radiator warm at the top, cold at the bottom

Is this your problem?

What to do

1. Turn the heating off.
2. Let the system cool for 30 minutes.
3. Bleed the radiator using a radiator key until air stops and water runs steadily.
4. Top up boiler pressure to around 1.2–1.5 bar if needed.
5. Turn heating back on and recheck.

Safe DIY if you’re comfortable bleeding radiators.

Stop if water doesn’t come out or pressure keeps dropping — that’s not normal.

Radiator stone cold, even after bleeding

Is this your problem?

What to do

1. Turn heating on fully.
2. Close the lockshield valve on all other radiators (turn clockwise).
3. Leave only the cold radiator open.
4. Wait 20–30 minutes to force flow through it.
5. Slowly reopen the other radiators one by one.

This is rebalancing — very common in UK systems.

Safe DIY if you take it slowly.

Radiator only heats when others are turned off

Is this your problem?

What to do

1. This points to poor system balance or low pump flow.
2. Check boiler pressure first (top up if low).
3. Try basic rebalancing as above.
4. You may also notice radiators heating unevenly

If it keeps happening, stop here.

Call a heating engineer — pump speed, system balance, or sludge may be involved.

Radiator cold on one side only

Is this your problem?

What to do

1. Gently tap the thermostatic radiator valve (TRV) head.
2. Remove the TRV head (usually unscrews by hand).
3. Check the small metal pin underneath moves freely.
4. Press it gently a few times until it springs back.

Safe DIY. Very common after summer.

If the pin won’t move at all, the valve needs replacing.

Radiator cold and pipes to it are cold too

Is this your problem?

What to do

1. This often means sludge blockage in that radiator.
2. You can try rebalancing, but it usually won’t fix heavy sludge.

Stop DIY here.

This needs a professional flush or radiator removal and cleaning.

What this usually costs to fix in the UK

• If the fix is air, a stuck valve, or simple rebalancing, most UK plumbers charge £60–£100 for a call-out and quick fix.
• If the thermostatic radiator valve (TRV) needs replacing, expect £120–£180, including parts and labour.
• If the radiator is sludged and needs removing and flushing, costs are usually £150–£300, depending on size and access.
• If the problem points to system balancing or pump issues, allow £90–£150 for investigation and adjustment.
• If you’re quoted £400+ for a single cold radiator without clear explanation, pause and get a second opinion.
• Most single-radiator problems in UK homes are fixed within one visit.