How to drain a radiator
By Tom Drake | 7th October 2024 | 4 min read
1. Turn off central heating
Before you can drain your radiator, you need to turn off your central heating and let the water in the system cool down.
When draining a radiator, you’ll come into contact with water as you loosen the valves. There’s a risk of scalding yourself on this water if you don’t allow your system to cool down first, so make sure your radiators and pipes have cooled completely.
2. Close the TRV valve
The TRV, also known as a thermostatic radiator valve, controls the temperature of your radiator. It is distinguishable from other radiator valves by the numbers on the front. To close the TRV, simply turn it to zero. If your radiator has a manual valve to control temperature instead of a TRV, turn it clockwise to close it.
3. Close the lockshield valve
With the TRV closed, move to the other side of the radiator and close the lockshield valve.
To close the lockshield valve, you’ll first need to remove the cap. You may be able to pull the cap off, but if there’s a screw in the top, remove it with a screwdriver first.
With the cap removed, use a pair of water pump pliers to turn the valve clockwise until it’s completely closed. Make a note of how many turns of the lockshield are required to shut it off. Turning the valve by the same number of turns when you switch your radiator back on will help keep your system balanced.
With both valves switched off, use a radiator bleed key to open the bleed valve at the top of the radiator. When you do this, a small amount of water will come out. If this water stops, you can be confident that the valves are preventing more water from entering the radiator.
4. Loosen the TRV nut
With both valves switched off, you can begin to drain the water from your radiator. This involves loosening the nuts which connect the radiator to the valves on both sides. Starting with the nut securing the TRV, place a bowl or container underneath the nut you’re going to loosen to catch the water. Some old towels to mop up any excess water can also be helpful.
Using an adjustable wrench, slowly loosen the nut that connects your radiator to the valve (not the nut that connects the valve to the pipe). It may also be helpful to steady the valve using a pair of water pump pliers. As you loosen the valve, water will start to flow out of the gap between the radiator and the valve. Don’t loosen the nut fully yet; you may need to retighten it to empty your container if it becomes too full.
If you closed the bleed valve earlier, open it again. Opening the bleed valve lets air into the radiator, which will help the water drain. Keep loosening the valve until the water has stopped flowing.
5. Loosen the lockshield nut
Once water has stopped flowing on the TRV side, you can repeat the process on the other side of the radiator. Grip the valve with your grips, then loosen the nut connecting the radiator to the valve with an adjustable spanner until water starts flowing. As with the TRV nut, keep loosening until the water stops flowing.
7. Tilt to drain excess water
With the valves disconnected, place a bucket or container next to one of the radiator outlets and tilt the radiator towards it. This will drain the water that’s sitting at the bottom of the radiator. If your radiator is particularly large or heavy, make sure you have some help with lifting.
Sludge that's accumulated inside your radiator can also come out at this point, so you may want to put sheets down to protect your flooring.
Draining a radiator FAQs
Can you drain a radiator without draining your central heating system?
If the valves on your radiator stop water from entering it when they’re switched off, you can drain a radiator without draining your central heating system. However, if you want to change the valves on a radiator, you’ll need to drain the system.
How do you reconnect a radiator after draining?
To reconnect your radiator, reattach it to the valves using the steps above in reverse, then open the valves on both sides to allow water back into the radiator. Remember to turn the lockshield valve by the same number of turns used to turn it off. Once the radiator starts to refill, open the bleed valve to release excess air.
Can you drain a radiator yourself?
With the right preparation and knowledge, you can drain a radiator yourself. However, it’s always useful to have someone to help, especially when lifting the radiator.
