Because we don’t use our radiators every day of the year it’s hard to tell if they’re working as well as they should be until you really need them. This can be hugely inconvenient, as well as potentially making your home cold when temperatures drop.

If you find yourself in this situation, it’s handy to have a guide to help you find the problem or know when it’s time to call an engineer to repair your boiler

In this article, we’re going to answer some commonly asked questions to help you with your central heating problems. However, some of our advice does include hands-on maintenance. If in any doubt, it’s always advisable to contact a professional to repair any faults.

What do you do if one radiator is cold?

Firstly, is your central heating switched on? After summer, it’s an easy thing to overlook, so check this first.

If you’ve turned up your thermostat and made sure all your radiators are switched on, this is a great way of checking for a localised problem. Working this out at an early stage, it can mean saving a lot of time looking for problems elsewhere, such as the whole radiator system or the boiler.

If one, or sometimes two, radiators aren’t heating up, it’s highly likely that trapped air is the cause. While radiators are out of use in warmer months, air can get trapped through small leaks or the pump above the supply pipe.

If you find the radiator is cold in certain places but warm in others, trapped air can also be responsible, however, there might also be debris blocking the heat — more on this later. If you’re testing the heat of the radiator, be careful, especially when the heat is turned up, in case of potential burning. Use a cloth to protect your hands.

How do you remove air from a radiator?

If you’ve identified which radiator isn’t functioning properly, and it’s possible that there is trapped air, it’s best to bleed the air out. Bleeding a radiator is usually a simple, quick and inexpensive process.

How to bleed a radiator

There are two ways of bleeding a radiator, depending on its age, which means adjusting the valve. This is the part that usually has a plastic cap. For older radiators, a radiator valve key is needed. It’s probably in that one kitchen drawer with the bottle openers and candles! If you can’t find one, you can buy them fairly cheaply from hardware and DIY stores. For newer radiators, a flathead screwdriver will work.

Before starting, keep a towel handy as water may start running from the valve. The radiator valve is usually found on one particular side.

  1. Turn the key, or screwdriver, anticlockwise to loosen the valve.
  2. Keep going until you hear the hiss of escaping air.
  3. Leave the valve open until the sound of the air being released stops.
  4. When water begins to trickle from the valve, start to turn the key or screwdriver clockwise to tighten it.
  5. The radiator should now be bled, which you can test by putting the heating back on.

Can you bleed a radiator when the heating is on?

Make sure the central heating is turned off when bleeding a radiator. Also, if the heating has been on, leave the radiator for long enough for it to be completely cooled down. The water inside the radiator may still be hot, even scalding, for a little while after the heating is switched off.

How often should you bleed radiators?

You should bleed your radiators once a year (even if they're working properly), ideally in September before they start being used frequently. You might also need to let out trapped air if you have noisy radiators which are making banging, clanking or gurgling noises.

How to unblock a radiator

The process of unblocking a radiator means completely removing it and taking it somewhere to be cleaned out, either in a garden or yard (or outside on the front steps if you have understanding neighbours).

Before starting, turn off the central heating and wait for it to cool down completely. Because there’s a likelihood of mess from a build-up of dirt inside the radiator, as well as water, put down towels and cloths under the radiator and around the pipes. It’s also a good idea to put a bucket under the radiator valve.

Close the valve using an adjustable wrench by turning it clockwise around the valve nut. However, it’s important to take note of the number of turns when closing the valve, as you will need to turn the nut by the same number when putting the radiator back.

  1. If you haven’t already, make sure to bleed the radiator using the process above.
  2. With the valve closed, remove the radiator, and take it outside.
  3. The most effective way of flushing a radiator is to use a hose to spray out all the dirt, which is mostly traces of rust, scale and dirt build-up. If you need to, you can also tap the radiator to loosen more dirt. Try to use something soft, so as not to dent or damage the radiator itself, such as a wooden mallet wrapped in a towel.
  4. With the radiator flushed out, and dried, you can reattach it.

What are the signs of a clogged radiator?

Continual problems with a radiator not heating up properly might be down to a build-up of debris in the radiator itself. A clogged radiator can show the same sort of problems that a radiator with trapped air might have, such as cold spots or not warming up at all.

Why are my downstairs radiators not working?

Again, if you’ve checked the central heating has been turned on and you have little or no heating, this will need further investigation. If you’ve found that more than one radiator isn’t coming on, there are other areas to look into.

Central heating pump

Radiators above the ground floor tend to be closest to the boiler. Because of this, these radiators will often get hot water pumped to them first. If the heat isn’t travelling far from its source, and not warming other radiators (especially on a lower floor), it’s likely to be down to the central heating pump. If the problem persists, it might be time to call out an engineer.

Diverter valve

With some hot water systems, if hot water from a tap is running, a diverter valve will take the water from the heating to the tap. If the hot water is running from the taps, but you’re getting no heat from your radiators at any point, it’s possible that the valve may be stuck in one position. Again, a job for an engineer.

We hope this has helped with troubleshooting to avoid unnecessary call-outs. If problems persist, this could be down to some other issues with your boiler or controls, and it might be time to contact a heating professional — if you need to book a repair, you can easily organise your repairs, plans and appliances in My Account. If you don’t have one, it’s also simple to create a new account.

About the author

Ian Palmer-Smith

Ian is our go-to expert when it comes to plumbing, boilers and carbon monoxide safety. After 39 years (and counting) of working in operations – he knows quite a bit about appliance maintenance and repairs too. Even during washing machine debates (yes, they happen), his expertise is unmatched. Thankfully, Ian regularly contributes to the blog to share his wisdom – helping us all out when our appliances aren’t working quite as we expect.

Last year, Ian was recognised as a finalist in the Institution of Gas Engineers and Managers’ Gas Leadership Award – a real testament to his authority in the industry. He’s even represented Domestic & General at the House of Commons. There he informed everyone about the importance of carbon monoxide safety and awareness in the home.

Outside of work, Ian is usually occupied taking his sons to various sporting events, watching  football, rugby… and a little more sport.

Explore Ian’s wealth of knowledge on all things gas safety and appliance care now. You can check out some of his insightful articles below.

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