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Flush a Central Heating System

How-to guides

What Does Flushing A Central Heating System Mean?

Over time, many central heating systems will gather debris and other unwanted materials throughout the various radiators and pipes in your home. As your system is always drawing in and circulating water, it is highly likely that your system will have at least some debris inside over sustained operation.

When this build-up becomes too great, the performance of your system can be adversely affected, resulting in loss of performance, unreliable heating, and other issues such as unwanted noise from your boiler or cold spots across individual radiators. This can be avoided through the process of flushing your system.

In brief, flushing a central heating system is the process of emptying the system of water and cleaning the interior. There are a number of ways to achieve this, the most common of which is ‘Powerflush’, which uses a device to do the vast majority of the work. Otherwise, you’ll need to manually flush the system yourself, which we will guide you through in this guide.

IMPORTANT: Flushing a central heating system is an involved task and requires some working knowledge of your central heating system to be done safely and correctly. Wherever possible, we recommend contacting a boiler engineer who can perform this task and properly maintain your boiler too.

When and Why Should I Flush My System?

It can be difficult to know exactly when you should flush your system, though there are a few key factors that can signal it’s time for a thorough system flush.

If you experience any of the following, it’s likely that you need to flush your system:

• Odd or unwanted noise coming from your boiler during operation

• Lengthy heating times beyond typical times

• Cold spots across your radiator

• Generally poor heating performance

By flushing your system, you stand to improve overall heating efficiency and safeguard your central heating system from any long-term damage.

How To Flush A Central Heating System

There are two main methods of flushing a central heating system - Powerflush, and manual flushing. Each has its own process, which we will walk you through in this section.

How To Powerflush A Central Heating System

Powerflush is the process of using a specialised device to pump cleaning chemicals into your system, circulating them and removing the unwanted material from the system itself. The chemicals are pumped at a high pressure to ensure any rust, corrosion, sludge, or miscellaneous debris is effectively removed. Generally, a Powerflush will take around 8 hours to complete fully, though a portion of this time is dedicated to the system pumping around the entire central heating loop. Particularly large or complex heating arrangements can take much longer to complete.

We do not recommend users to Powerflush a system, as it requires the use of specific chemicals for the job and a dedicated machine to do so. As this requires additional knowledge about your heating system, as well as complications from varying types of systems, this is best tackled by a trained heating engineer.

When an engineer comes to Powerflush your central heating system, they will follow a number of steps:

1. Protect Your Floor and Home From Water

They should lay down protective sheets and a container to capture any escaping water before beginning any flushing activities. This will need to be placed beneath the location where they will connect the Powerflush machine.

2. Connecting the Machine to Your System

The engineer will then take the necessary steps to connect the Powerflush machine. The exact process will change depending on the needs of your system, though they will need to completely empty the system to allow the pumps to be properly connected.

3. The System Will Be Flushed

At this stage, the engineer will begin the process of flushing the specialised chemicals throughout your whole central heating system. This will be done multiple times and often in both directions to ensure the best results. The debris, sludge, and other material inside, should be flushed out as this process continues. If individual radiators are in particularly bad shape, they may work on this separately to ensure the best results.

4. Refill the System and Finish

Once sufficiently flushed, the engineer will refill the system with clean water, whilst often adding an inhibitor solution to reduce the likelihood of build-up within your system. Your system will now be ready for use again as normal.

How To Manually Flush A Radiator

If you don’t have a Powerflush machine available, you can manually flush radiators individually to remove debris and improve performance. This can be particularly beneficial if you have only a specific radiator that is exhibiting poor performance.

This process is best performed by a professional engineer to ensure that your system is flushed effectively and with minimal complications.

To manually flush a radiator, you need to follow a number of steps:

1. Protect your Floor and Home from Water

You should lay down protective sheets and a container to capture any escaping water before beginning any flushing activities. This will need to be placed beneath the location where you will bleed and remove the radiator. Also ensure that before you begin any work on your heating system, you turn it off and it has gone fully cold.

2. Bleed and Remove Radiator

In order to flush the radiator, you will need to remove it from the system. To do so, close off both valves on either side of the radiator - TRV and lockshield as appropriate - and bleed the radiator to remove excess water and then disconnect it from the two connecting pipes. Make note of the valves position at this point so you can easily return them to their current values upon reconnecting the radiator.

Once you have sufficiently removed any lingering water from the radiator itself, you can disconnect it from the pipes and remove it from the system.

3. Use a Hose and Water Source to Flush the Radiator

At this point, you will want to take the radiator outside. You will want to place your hose or water source onto the inlet valve of your radiator, turning on the water supply to the hose and flushing the radiator out. Continue to run water through the radiator until all the water exiting the radiator is clear and free from sludge or debris.

4. Reconnect the radiator to the system

You can bring the radiator back inside and reconnect it to the central heating system, reversing the steps you took to disconnect it. Ensure you return the valves to their original positions. We also recommend opening the bleed valve to ensure any trapped air is exhausted from the system.

Follow this process for each radiator you wish to flush and you will have successfully flushed your radiators.

We would always recommend any work on your central heating system be undertaken by a professional engineer in case of complications.


Flushing a central heating system can be an involved and difficult task, though the benefits of doing so are absolutely worth it for the efficiency and long-term health of your home heating system. We do recommend contacting an accredited professional to perform this task where possible, as you will have added peace of mind in knowing the work is undertaken safely and effectively.

Scott Flannigan

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