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Why is my radiator not heating up?

A radiator that stays cold usually has a closed or stuck valve, trapped air, sludge in the pipes or a heating system that is out of balance. You can check the valve settings yourself, but anything that means opening the system or touching the boiler is a job for a heating engineer.

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By the QuoteZila editorial team. Editorial policy.

What does it mean when one radiator stays cold?

If the heating is on in a Cheshire home and one radiator stays cold while the rest warm up, the boiler is probably working and the problem sits somewhere between that radiator and the pipes that feed it. If every radiator is cold, the cause is more likely the boiler, the pump or the controls, and that needs a heating engineer straight away.

QuoteZila is starting in Cheshire, with Crewe, Nantwich and Sandbach among the first towns. Anyone in the UK can post a job or register a business. This page explains the usual causes in plain words so you can describe the fault clearly when you ask for help.

Is the valve closed or stuck?

Most radiators have two valves, one at each end. One is often a thermostatic radiator valve with a numbered head. The Energy Saving Trust says most of these valves have a numbered dial, and that lower numbers mean a cooler room and higher numbers a warmer room [S1]. The numbers are not the same temperature on every model. If the head has been turned right down, the radiator can stay cold.

Turning the head up is a safe first look. If the head is already on a high setting and nothing changes, the pin under the head may be stuck after a summer of not moving. Freeing it can be simple, but forcing it can break the valve. A heating engineer can free it or replace the valve.

The Energy Saving Trust says radiator covers can stop the valve sensing the room temperature accurately, because they trap warm air around it [S1]. Moving a sofa away from the radiator costs nothing and is worth trying.

Is air or sludge the problem?

Where the cold patch sits gives a clue:

  • Cold at the top, warm below. Air has probably collected at the top. Letting it out means opening a valve on a system that holds water under pressure. Many sealed systems then need the pressure brought back up at the boiler.
  • Warm at the top, cold at the bottom. Sludge, a mix of rust and debris, may have settled in the lower channels. It does not clear on its own.
  • Cold all over, while its neighbours are hot. A stuck valve, a blocked pipe or a system that is out of balance is more likely.

None of those clues is a diagnosis. They help you describe the fault so that a heating engineer can quote for the right job.

Is the heating system out of balance?

On a system that is out of balance, the radiators nearest the boiler take most of the hot water and the furthest ones barely warm up. It often shows up after a new radiator is added or a valve is changed. Balancing means adjusting the lockshield valves across the house, one by one, while the system runs. It takes time and patience rather than parts.

Adding or replacing radiators can be part of work that needs building regulations approval. GOV.UK lists installing or replacing a heating system and adding radiators among the jobs that may need approval, and says you do not need to arrange it yourself if the installer is registered with a competent person scheme [S3]. Ask the engineer how they will handle that if new radiators are part of the fix.

When should I stop and call someone?

Call a heating engineer if:

  • every radiator is cold, or the hot water has stopped too
  • the boiler shows a fault code, or its pressure gauge reads very low or very high
  • you can see water on the floor, around a valve or under the boiler
  • the radiator was replaced or moved recently and has never heated properly since

Do not take the boiler casing off and do not try to repair the boiler. HSE says it is illegal for anyone to use a gas appliance they suspect is unsafe, and that it should be turned off and left alone until a Gas Safe registered engineer has checked it [S4]. If you smell gas, call the gas emergency line. You can look up an engineer on the Gas Safe Register before you book.

Gas Safe Register. QuoteZila is not affiliated with this organisation.

Jobs you might post

These are examples, not taken from real job posts.

  • "Back bedroom radiator stays cold even with the valve on six. The rest of the house heats fine."
  • "Two downstairs radiators are cold at the bottom. The house is about thirty years old and the system has never been cleaned."
  • "We added a radiator in the extension and now the upstairs ones barely warm up."

Say how old the boiler is, whether it is a combi or has a hot water cylinder, and which radiators are affected. Photos of the boiler display and the valves help.

How to compare quotes for a cold radiator

Citizens Advice suggests getting written quotes from at least three traders, and explains that a quote is a fixed price while an estimate is only a guess [S5]. For a heating fault, ask each engineer to say what they think the cause is, what they will do first and what happens if that does not work. A powerflush, a radiator swap and a stuck valve are very different jobs.

QuoteZila is free for customers and local businesses [QZ1]. Up to five matched local businesses can send you a quote [QZ2].

Honest status: QuoteZila is new. We're starting in Cheshire, beginning with Crewe, Nantwich and Sandbach, and growing area by area. Anyone in the UK can still post a job or register a business. How fast you get quotes depends on how many local businesses have joined near you. Businesses can register and receive jobs straight away. We don't check insurance, qualifications or registrations, so please check these yourself before you hire.

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See heating engineers and plumbers for what each trade covers, or the plumber cost guide for how call-out and hourly prices are usually set out.

Questions about cold radiators

Why is my radiator cold at the top but warm at the bottom?

That pattern usually points to air collecting at the top of the radiator. Letting the air out involves opening a valve on a pressurised system, and on many homes the boiler pressure then needs topping up. Ask a heating engineer to do it if you are not sure how your system works.

Why is my radiator warm at the top but cold at the bottom?

A cold lower half often means sludge has settled inside the radiator or the pipes. Clearing it can mean a chemical clean, a powerflush or taking the radiator off the wall. That is engineer work, and the quote should say which method they plan to use.

Can I fix a cold radiator myself?

You can check that the valves are open and that the thermostatic valve has not been turned right down. The Energy Saving Trust says most of these valves have a numbered dial, with lower numbers meaning a cooler room and higher numbers a warmer room. Anything that means opening the system, draining it or touching the boiler should go to a heating engineer.

Do I need a Gas Safe engineer for a cold radiator?

If the fault is in the boiler or its controls, yes. HSE says anyone employed to work on gas appliances in a home must be on the Gas Safe Register and competent for that type of work. A radiator-only job may be done by a heating engineer, but ask what they will touch.

Does QuoteZila check the businesses?

No. We don't check insurance, qualifications or registrations, so please check these yourself before you hire. You can report a quote or a business from your job page.

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Sources

  1. QZ1: QuoteZila product fact. QuoteZila home and jobs-for-tradesmen copy.
  2. QZ2: QuoteZila product fact. QuoteZila FAQ and app README.
  3. S1: Heating controls, Energy Saving Trust. Accessed 2026-10-25. https://energysavingtrust.org.uk/advice/thermostats-and-heating-controls/
  4. S2: Domestic gas: frequently asked questions, HSE. Accessed 2026-10-25. https://www.hse.gov.uk/gas/domestic/faqs.htm
  5. S3: Building regulations approval, GOV.UK. Accessed 2026-10-25. https://www.gov.uk/building-regulations-approval
  6. S4: Gas safety: home owners, HSE. Accessed 2026-10-25. https://www.hse.gov.uk/gas/domestic/faqownerocc.htm
  7. S5: Before you get work done on your home, Citizens Advice. Accessed 2026-10-25. https://www.citizensadvice.org.uk/consumer/getting-home-improvements-done/before-you-get-building-work-done/