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how to drain down a heating system

How to drain down heating system – Complete guide

Your Ultimate Guide to Draining a Heating System



Keeping your heating system in good condition is essential for its efficiency and longevity. One crucial maintenance task is draining the system when necessary to remove any built-up debris or sediment. In this comprehensive guide, we will walk you through the step-by-step process of draining your heating system effectively and safely.



Understanding the Importance of Draining a Heating System:

Before we dive into the draining process, it’s important to understand why it’s necessary. Over time, sediment can accumulate in your heating system, leading to reduced performance and potential damage. Draining the system helps remove this sediment and ensures optimal functioning of your heating system.  Or you may just need to carry out some minor works.  We get it.

Preparing for the Draining Process:

1. Gather all the necessary tools: To start, you will need a bucket or container to collect the drained water, a hose, and any necessary spanner’s or grips.

2. Turn off the heating system: Before beginning the draining process, make sure to turn off the power supply to the heating system to prevent any accidents.

Draining the Radiators:

1. Start with the lowest radiators: Begin draining from the lowest radiators and work your way up. Connect the hose to the drain valve, ensuring it is securely attached.

2. Open the drain valve: Turn the drain valve anti clockwise to open it, allowing the water to flow out. Adjust the hose to direct the water into the bucket,
drain or container.


Flushing the System:

1. Turn off the water supply: When the system is draining.  With a tank fed system, we always allow water to replenish first, prior to turning the water off via the expansion tank.  Or header tank.  This ensures there are no block feeds.  Right, it’s time to flush the system. Locate the water supply shut-off valve and turn it off to prevent new water from entering the system.

2. Open the bleed valves: Open the bleed valves on each radiator to release any remaining water in the system. This will help remove any trapped air pockets.

Please Note: With all the necessary bleed valves open.  With any motorised valves manually opened.  When that hose stops running.  You’re drained!

Refilling the System:

1. Close all valves and bleed vents: Once the system is fully flushed or your task is complete.  Close all the drain valves and bleed vents.

2. Turn on the water supply: Turn the water supply valve back on to refill the system. Monitor the pressure gauge to ensure it reaches the appropriate level.  You may want to add an inhibitor prior to re-filling.


Testing the System:

1. Bleed air from radiators: After refilling the system, bleed the air from each radiator to ensure proper circulation.

2. Check for leaks: Inspect the system for any signs of leaks once the heating system is operational.

Handy tip alert!!… For heat only systems or systems with a hot water tank.  We urge you to run the hot water circuit only (not the taps, the setting “hot water” on the timer).  We find this is the best way to get rid of the majority of the air due to the initial drain down and re fill.

If you have a radiator or two fail to work.  This could be an air lock.  Click HERE to find out the best way of clearing this.




Draining a heating system is a crucial maintenance task that helps maintain its efficiency and prevent potential issues. By following the steps outlined in this comprehensive guide, you can drain your heating system effectively and ensure its optimal performance. Remember to take safety precautions, such as turning off the power supply and monitoring for leaks, to ensure a successful draining process.

Tom Hewitt
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