A Guide to Power Flushing Your Central Heating System

Summary: How to power flush your central heating system to clean it and make it more efficient. By flushing your central heating you will save money on heating bills by improving your heating systems effectiveness. Hire a power flushing pump and learn how to flush the system yourself in this project to save even more.

Don't want to do this job yourself? Let us help you find a tradesman local to you

The first thing you need to understand is what a Power Flush is.

A power flush is the process of cleaning out a central heating system by circulating high volumes of (forced) water and cleaning agents around a heating system to remove debris, rust etc.

You may need a power flush if you have cold spots in your radiators, or your radiators are cold at the bottom and warm at the top. Sometimes one radiator in your system may not be working at all and this is a sign that a flush may help.

If you have a lot of sludge in the feed and expansion tank or the heating system is very slow to warm up these are both indicators that a system clean is required. Another indicator of the need for a power flush is if your thermostatic radiator valves are stuck in the off position.

Power flushers come in sizes which range from a 20 litre tank which is enough for a 25 radiators to a 200 litre tank which will keep going for the largest of commercial properties. The power flushing pumps can be hired from your local tool hire shop. Many pumps have an instantaneous flow reverser to make life easier.

To start a power flush on a central heating system you will need to isolate your power supply to the system. Do not remove your earth continuity bond. Close both isolating valves that you should have either side of your central heating pump. You are then in a position to be able to remove the pump from your system. You can now connect your power flush system to your central heating system if your power flusher comes with connecting manifold.

With cheaper options you will be limited to connecting your power flush to your central heating system via your radiator valve tails.

Turn off your radiator valves, disconnect one, allow the air bleed valve (the one used to bleed radiators) to be open so air can come into your radiator and water out from the disconnected valve.

When all the water has been removed from the radiator you can now connect your power flush to the return valves on the tails of your central heating.

Note: Once you are ready to remove your disconnected radiator you will have to continue the continuity of the earth bonding before you remove the radiator this is an obvious safety precaution.

If your system is a open vented system you will need to turn off the mains valve. If for any reason like your stop cock is jammed or broken as this sometimes happens, you can go to your header tank and tie up the floating ball valve to stop the system refilling.

You can now go through a little check list to make sure you are ready to power flush.

  1. Switch off boiler
  2. Open your radiator valves fully
  3. Diverter valve fully open
  4. Close off your water supply
  5. If you have a sealed system you will need to de-pressurize system, drain off some of the water contents to bring the pressure to atmospheric pressure. Cap of the expansion pipe to the feed and expansion tank and also the cold downfeed pipe from the feed and expansion tank.
Capping off pipes to and from feed and expansion tank

Capping off the vent pipe and downfeed pipe to the feed and expansion tank for power flushing the central heating system

You are now ready to power flush:

Make sure your dumping and overflow hoses go outside to a suitable drain or waste area.

You can add your cleaning fluid to the power flush device. Check again to make sure all radiator valves are open. Switch your power flush unit on so water is circulating around your heating system.

Turn on boiler to generate heat so chemicals start their process of cleaning, turn off boiler when heat of water has reached about 45°. Reverse the power flush flow every 10 minutes.

Close all radiators except one and allow it to flush through, repeat this process with every radiator.

Now open all radiator valves and let the flush flow freely. When the system has been flushed out and you have clean running water coming out, add neutralizing agent to neutralize the cleaning process.

Do one more complete flush then add a corrosion inhibitor. Let this circulate then close all valves, disconnect the power flush unit, reconnect all items of the central heating system and release all valves to open and turn on water mains.

Your central heating system is now ready to use again.

As always DIY Doctor always recommends the use of correct safety and protective equipment.

Don't fancy doing this project yourself? We work with Checkatrade to ensure that we recommend only reliable and trustworthy tradesmen.

All project content written and produced by

Project Feedback