8 reasons why your radiator isn't heating up

When your radiators suddenly stop doing their job, it’s easy for frustration to set in - especially when you’re relying on them to keep your home warm and comfortable. The good news is that most radiator issues have straightforward causes and simple solutions. In this blog, we break down the most common reasons radiators fail and show you how to get them working efficiently again.

Top causes why your radiator isn't working (and how to fix them)

Let's go through the most common reasons why one radiator in your home might stop working:

Leaking radiator

Your radiator may be leaking due to common issues like corrosion in the system or loose or worn valves and fittings. Before calling a professional, you can try to repair the leak yourself:

• Get a bucket and some old towels - without these, things could get messy!
• Dry the radiator with a towel and use some tissue paper to check every joint and valve to find the source of the leak
• If the valve at the bottom of your radiator is leaking, the packing around its spindle might be worn.

How to repair a leaking radiator valve

1. Drain the system. Turn off the supply valve (where water enters the radiator) and the plastic-capped lockshield valve (count how many turns it takes). Use towels and a bowl to catch any excess water.
2. Undo the union nut (connects the valve to the radiator itself, quite large, usually hexagonal) between the feeder pipe and radiator.
3. Open the bleed valve to allow the remaining water to run off into the bowl.
4. Wrap the valve tail with PTFE tape (plumber's tape, used to seal leaks) 10-15 times. You can get PTFE tape from any DIY store.
5. Retighten the union nut and open the bleed and lockshield valves (remember how many turns it took).
6. Once water has returned to the system, check again for leaks and close the bleed valve.

If the leak is coming from a hole within the radiator itself, you'll need a new radiator altogether. Isolate the radiator by closing the supply and lockshield valves to prevent leakage until you find a replacement. Check out our radiator buying guide for tips on how to choose the best radiator for your needs.

Air pockets in the radiator

If your radiator feels cold at the top but warm at the bottom, there may be some trapped air in the system. This could also cause your radiator to become noisy.

If this is the case, don't worry, there's an easy fix! All you need to do is release the trapped air. See our step-by-step guide on how to bleed a radiator to help you do this.

Sludge, debris or blockages in the radiator

If the radiator is cold at the bottom but warm at the top, it suggests that there is debris, a blockage or sludge sitting at the bottom of the system, stopping hot water from circulating and heating this section up.

To clear this out, your radiator needs to be power flushed. Call a plumber to do this safely; it's not something you should attempt to do on your own.

The thermostat isn't working properly

If the whole radiator is cold, the issue might be as simple as the thermostat being switched off. Check that it's set to a warm temperature - if it is and the radiator is still cold, the valves might have seized up in the closed position.

How to check if the thermostatic radiator valve has seized

1. Remove the plastic top cover from the valve
2. Undo the knurled nut (a fastener with a textured, ridged outer surface) that is used to secure the valve. You can do this with your hand.
3. Check that the centre pin can move freely, up and down a few millimetres.
4. If it doesn't move, it's seized up.
5. Try applying some penetrating oil (like WD40) and tapping it gently or wiggling it with pliers to get it moving again.

If the pin won't budge after trying this, you'll need to call a professional to replace the valve altogether.

Multiple radiators aren't working

If more than one radiator isn't working, you may suspect there's a bigger problem at play, but it's worth checking if your heating is switched on before panicking! If there's still a problem, it may be one of the following issues causing it:

Low boiler pressure

If the heating is switched on as it should be and there's still an issue, it could be because the boiler pressure is too low, so it can't provide the hot water needed to heat the house. Learn how to check your boiler pressure and top it up if needed in our boiler pressure guide.

Faulty diverter valve

The motorised diverter valve controls the flow of warm water to your heating and taps. It prioritises hot water flow to the taps - so if you've got hot water but no central heating, it's probably because there's an issue with the diverter valve and it may be stuck. Don't try to fix this on your own, it's best to call a gas safe boiler engineer to arrange a repair.

If you're having issues with both heating and hot water, check out our top tips for what to do before calling a professional.

New radiator not working

Just had a brand new radiator installed, but it's not heating up? It could be as simple as some trapped air in the system or incorrect valve settings. Try bleeding your radiator and check that both the thermostatic radiator valve and lockshield valves are open to allow hot water to flow through.

Radiator not working after bleeding

If you've bled your radiator but it's still not heating up, you may have done it wrong. Check your boiler pressure to make sure it's not too low, before bleeding your radiator again - sometimes air can move around the system after the first bleed. Follow our step-by-step instructions on how to bleed a radiator to make sure you do it correctly.

If there's still an issue, check for any leaks in the system. Can't find any leaks? The system may need flushing to remove sludge or other blockages. Call a plumber to power flush your system to get it up and running again.

Radiator still not working?

If you've tried the above fixes and are still having issues, or don't feel confident to try them yourself, you can always call one of our gas-safe engineers on 0800 497 0705⁽¹⁾ to come and take a look.

And if your heating problems keep coming back, it could be a sign that your boiler is ready for an upgrade. Get a new boiler today and enjoy warmer rooms and total peace of mind.

Want an instant boost while you wait? Consider adding electric radiators for quick, efficient heat exactly where you need it - the perfect way to stay warm without the hassle of central heating.