How To Drain A Central Heating System

Rule out water leaks during repairs by following our six-step plan to drain your central heating system.
Written By: Richard Morgan | Updated:
How To Drain A Central Heating System
Richard Morgan/DIY Works

Whether you are repairing a leak or replacing a radiator, you may need to drain the central heating system in your home. Although it can be time-consuming, it’s good practice as it helps to remove any sludge or limescale build-up. It also gives you complete peace of mind that there won’t be any water leaks whilst carrying out the work.

Below are the steps required to drain a central heating system, with the photos taken from a recent radiator replacement on the top floor of my very own house.

What You’ll Need

  • Hose pipe
  • Adjustable spanner
  • Jubilee Clip
  • Radiator key
  • Towel (to clean any spillages)

How To Drain A Central Heating System

1. Switch Off The Boiler

Before you begin to fix any leaks or replace any radiators, you will want to ensure that you switch off the boiler beforehand. Although not technically necessary, it’s a safety measure that provides you with complete peace of mind whilst carrying out any repairs.

2. Connect The Hose Pipe

With the boiler switched off, you are now ready to drain the central heating system by first locating the drain-off valve. Once located, attach a hose pipe to the drain valve and secure it using a jubilee clip. If it isn’t securely attached, you risk dirty water from the central heating system spilling all over your floor.

3. Direct The Hose Pipe Outside

The next step is to direct the hose pipe outside your home, as we did in the photo below. If it doesn’t reach, we recommend buying a new hose pipe because it’s crucial to draining your central heating system.

How To Drain Central Heating System

Richard Morgan/DIY Works

4. Open The Drain Valve

Now that you have set up the draining of water, use an adjustable spanner to open the drain valve.

5. Open The Bleed Valves

To drain the water at a much faster rate, you can open the bleed valves of the radiators. Whilst you are opening them, you should be able to hear the air being sucked from the central heating system.

6. Check Water Is Draining Out

Once the drain valve and bleed valves are open, double-check that water is being drained from the central heating system. The length of time it takes to drain out completely can vary, but most systems take between 10 and 15 minutes.

Once you are happy that all of the water has been drained, you can close the radiator bleed valves. After that, you can proceed to close the drain valve and remove the hose pipe. However, whilst handling the hose pipe, be warned that there may be some water still inside of the pipe, therefore, walk straight outside with it.


Although it may initially seem daunting, draining a central heating system is relatively straightforward. As long as you securely attach the hose pipe, there should be no issues whatsoever and once drained, you can happily complete any repair work to the radiators in your house. If you have any questions, feel free to contact us, and we can provide our advice where possible.

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