How to flush a radiator to improve your heating and keep energy bills down

·6 min read
 white radiator on brick wall in living space
white radiator on brick wall in living space

If you know how to flush a radiator it will ensure your heating appliances run smoothly and efficiently. Just like how to unblock a toilet, there are do-it-yourself ways to carry out the job.

'If you don’t, it could mean that you are paying a higher heating cost for inefficient radiators that are not providing adequate heating for your home,' says Jessica Steele, heating technology specialist at Best Heating. 'With rising energy costs, this is the last thing any homeowner needs'. As a guide, you should be flushing radiators every five to six years to get the most out of their performance and keep your utility bills down.

There are also some tell-tale signs you can look out for that will reveal its time to flush your radiator such as: the appearance of cold patches at the bottom of your radiator; either brown or no liquid at all comes out when you bleed them; they are leaking; your boiler is making loud noises; or some radiators are not heating up as well as others in your home.

Why should I flush a radiator?

tall wall radiator in grey living room
tall wall radiator in grey living room

Flushing a radiator simply means flushing fresh water through the heating appliance to clean it and remove the build-up of sludge and dirt that is preventing it from doing its job properly, and are stopping you from saving energy at home.

'Sludge is made up of dust particles mixed with scale that circulates throughout the whole radiator system,' says Steven Pester of Resolve Plumbing Services LTD at Rated People. 'It normally happens when your radiator is really old or hasn’t been maintained properly'.

'As the sludge builds up it puts a strain on your boiler and can be one of the biggest causes of boiler breakdowns. However, by flushing your radiator, you can get rid of this build-up which allows for an even distribution of heat, helping your home heat up quickly and efficiently,' he says.

How to flush a radiator

black radiator on grey wall in shower room
black radiator on grey wall in shower room

Confident DIYers should be able to flush the radiators in their home themselves by following our straightforward 10-step guide below. Be aware that it is more involved than the process to bleed a radiator.

If you don’t feel comfortable carrying out the job yourself, always seek professional help from a Gas Safe Registered engineer.

1. Get the right equipment

To be able to flush a radiator make sure you have the following tools:

• A radiator bleed key

• A rubber hammer

• A spanner

You’ll also want old sheets and/or towels to mop up any sludge or water spillages that come out of the radiator and a bucket to catch water and dirt when you drain the heating system.

2. Turn off your heating

Black radiator on grey wall
Black radiator on grey wall

Next, you need to turn off the heating and allow your radiator to cool down to prevent burning yourself.

'Factor in an hour and a half for your radiators to cool down properly after you’ve switched them off,' says Matthew Jenkins at MyJobQuote.

3. Switch off the valves

Shut the radiator off from the rest of your central heating by turning off the valves at either end of the radiator.

To do this, turn the TRV (thermostatic radiator valve) off by hand by twisting it clockwise or to the ‘0’ position.

To turn the lockshield valve off, you will need to remove the plastic cap then use a spanner to turn the valve clockwise all the way.

'Make a note of how many turns it took to turn the lockshield valve off as you’ll need to turn it the same number of times the other way when you put the radiator back on the wall,' advises Matthew Jenkins.

Next, use a spanner to loosen the nut that joins the radiator to the TRV.

4. Use a bucket to catch water

Water may drip from the TRV, so place a bucket underneath to catch excess liquid. Next, use a radiator bleed key to open the bleed valve and remove any air pressure. 'Once all the air has been removed, water should start to leak out of the bleed valve,' says Jessica Steele.

5. Drain the radiator

low radiator under window
low radiator under window

Wait until all the water has drained from the TRV, making sure all the sludge and dirty water has been removed. Then loosen the nut on the lockshield valve with your spanner and tilt the radiator to catch any water out of that side too. Once drained, close the bleed valve with your bleed key.

6. Take the radiator off the wall

Now take the radiator off of the wall and move it outdoors where you can hose it down.

'It’s a messy job, so make sure you cover the radiator inlets with a towel or plastic bags while you carry it through the house as it will probably still have some dirty water and sludge inside,' says Jessica Steele.

CIPHE also advises asking a friend to help you carry the potentially heavy radiator outdoors, too, to avoid injury.

7. Flush the radiator

small radiator in kitchen
small radiator in kitchen

To get rid of any dirt still remaining in your radiator, you need to attach a hose pipe to the radiator valve inlet and turn the tap on full blast. The flow of clean water flushing through the radiator and out of the other inlet should bring all the sludge with it.

'Use your rubber hammer to tap the radiator and dislodge any remaining build-up of sludge,' recommends Jessica Steele. Repeat this process by attaching the hose to the valve inlet at the other end of the radiator to get as much sludge out as you can until the water runs clear.

8. Reconnect your radiator

Once clean, hang your radiator back on the wall, re-tighten the nuts and open both valves, remembering to turn the lockshield valve the same number of times as you did when removing the radiator. Open the bleed valve with your radiator key to allow any trapped air to escape from the air vent.

9. Check boiler pressure

Disconnecting your radiator can cause the boiler pressure to drop so you may need to top it back up.

'The boiler pressure should be between 1 and 1.5 bar. If the pressure has dropped below 1 you will need to re-pressurise the system using the external filling loop,' says Jessica Steele. Always refer to your boiler’s manufacturer’s handbook for advice on how to repressurise your boiler system.

10. Turn your heating system back on

white radiator on brick wall in living space
white radiator on brick wall in living space

Once you’ve completed all the steps above, switch your heating system back on and check that everything is working properly.

How much will it cost to hire a professional to flush the radiators?

Jessica Steele advises a full heating system flush will cost around £300 for the average home with six radiators. 'If you do choose to hire a professional plumber, they will likely give the system a chemical power flush to combat the blockage using specialist equipment,' she says.

How do you prevent sludge from building up in the system?

Matthew Jenkins advises adding more inhibitors to the heating system. 'It’s a chemical treatment that breaks down unwanted particles in the heating system. Be sure to keep an eye on the inhibitor levels and top it up whenever needed,' he says.