Heating on but radiators cold: what to check (UK troubleshooting guide)

If your heating is on but radiators are cold, it’s stressful, and it’s tempting to assume the whole system has failed. In reality, there are a few common causes, and some are simple checks.

1) Confirm the controls are actually calling for heat

It’s possible the heating is “on” according to the timer, but not actively heating.

Check:

• Is the programmer set to heating on (not hot water only)?

• Is it on AUTO (schedule) or ON (manual), not OFF?

• Is the thermostat set above the current room temperature?

• If you have a smart thermostat, is it in away/eco mode?

If the thermostat isn’t calling for heat, radiators can stay cold even though the schedule says “on”.

2) Check boiler pressure (if your boiler has a pressure gauge)

Low pressure can stop heating working properly on many systems.

• If your boiler has a gauge, see whether it’s in the normal range shown on the boiler/guide.

• If it’s low, follow the manufacturer instructions or call an engineer.

If you’re unsure, don’t guess, it’s fine to get professional help.

3) Check radiator valves and TRVs

Before anything else:

• Make sure radiator valves are open.

• Turn TRVs up and down to see if they respond.

• If a TRV pin is stuck, it may need freeing, but don’t force it.

A single closed or stuck valve can make a radiator stay cold.

4) Air in radiators (bleeding)

If radiators are cold at the top and warm at the bottom, trapped air may be the issue.

Bleeding radiators can help, but do it carefully:

• heating off

• radiator cooled

• cloth/container ready

If you’re not comfortable doing it, a heating engineer can handle it quickly.

5) If some radiators heat and others don’t

This often points to:

• balancing issues

• circulation/flow problems

• valve issues

You can gather useful information:

• Which radiators heat first?

• Are the furthest radiators cold?

• Is it the same pattern every time?

That information helps an engineer diagnose faster.

6) When to call an engineer

Call a qualified engineer if:

• the boiler shows repeated fault codes

• pressure keeps dropping

• there are leaks

• radiators stay cold after basic checks

• the issue is recurring

Conclusion: start with controls, then move to system checks

When heating is on but radiators are cold, start with the basics (controls, thermostat, valves), then check pressure and radiator issues. If it’s not straightforward, a professional check is the safest route.

If you’re considering longer-term options for better room-by-room control, Trust Electric Heating can help with a free quote and practical guidance.

Call 0800 5999 109 or email [email protected] for more information or a free quote.

Scott Conor

Chief Technical Officer

In 2012, Scott founded Trust and invented the NEOS electric radiator after finding a gap for a more innovative and cost-effective electric radiator within the industry. He’s the driving force behind Trust’s research and development, using market-leading strategies to keep customers warm.

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Tags: General Guides.