Category - Boilers
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Will Scholfield, Engineer

31 Jan : Updated 4 Apr ● 4 min read

How to drain a central heating system

A central heating system is an integral part of every home as it provides both hot water and heating to the property. Regular maintenance of your central heating system is essential to maintain its performance and prolong its lifespan, saving you money long term. 

Do you know exactly how to drain your central heating system? BOXT have prepared this step-by-step guide to help you out. With the right tools and know-how, anyone can drain a central heating system, though if you would prefer professional help, get in touch with one of our specialist engineers. 

When should I drain my central heating system?

You should drain your central heating system to maintain it from time to time. By not draining it, you risk the system having issues, and issues cost money. 

It should be drained when installing a new radiator, removing an old one, or putting an inhibitor into the system. An inhibitor is a solution used to stop rust affecting your central heating system’s performance. 

A step-by-step guide to draining your central heating system

  • Switch off the system

Before you begin you should switch off the system completely for safety reasons. You should also allow time for the water in the pipes to cool down. 

  • Turn off the water supply to the boiler

It is important that you turn off the water supply to the boiler as this prevents any water from entering the system whilst you are draining it. To do this, turn the stop tap. 

  • Find the radiator with the drain-off valve

Locate the radiator in your home with the drain-off valve. This is usually on the first floor of your home. When you have located it, using a jubilee clip, attach a hosepipe to it, and drain the water outside. If you choose to use a bucket, make sure you shut the valve every time you empty this to prevent any spillages.

  • Bleed the radiators 

Now you can bleed the radiators. Open up the valves on all radiators throughout your home, starting with the ones on the top floor to make the water drain out faster. Wait around 10-15 minutes before opening the valves downstairs. 

Open up the bleed valves on all radiators to let the air out of the system; the water will drain out more quickly. 

Return to the radiator you attached the hosepipe to and open up the valve. The water will begin to drain out of your central heating system. This can take up to an hour, depending on the system you have. 

  • Complete the process 

Once you are confident that the process has finished and all of the water is out of the system, tighten up the valves on all of the radiators, close the valve on the radiator you started with and remove the hosepipe. Prepare a container in case of any extra water spilling out whilst removing this. 

That’s it! You now have the skills to drain a central heating system. 

But what if I don't have a drain valve? 

If you don't have a drain valve, you should follow step 1 and 2 of the step-by-step guide and then: 

Isolate the radiator from the system 

To do this, close the two valves and rotate the regulator in a clockwise direction. You should then remove the plastic cap off of the lockshield and close the valve up tightly using pliers. 

Open up the bleed valves

You can then open up the bleed valves on all of the radiators to let the air out of the system and speed up the process. 

Loosen the nuts and drain

Loosen the coupling nut on the regulator side of the radiator. Place a container under the radiator and rotate the nut counterclockwise until the water begins to drain. When the radiator valve is in an off position you can attach a hosepipe however this will need a special fitting. This will then drain the central heating system. 

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