Easy Guide: How To Flush A Pressurised Central Heating System

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At Grand Union, we specialise in helping our customers with central heating repair in Milton Keynes and the surrounding areas. We are specialists in radiator replacement in Newport Pagnell and we are recognised heating specialists in Buckinghamshire and surrounding counties. 

We know though, that there are a lot of you out there who will have a go yourselves and for you we have put together this handy step-by-step guide to help you carry out a problem free pressurised central heating system flush.  If you need us, however, we are the go to heating specialists in Northamptonshire and all surrounding areas and we will always be happy to carry out the work for you. 

Before you start, identify which system you have.  A sealed system will feature a pressure gauge, situated on the boiler.

You will need to understand how the boiler and your heating system work. You will also need to be able to connect and disconnect a radiator from your system. Once those boxes are ticked this is our 16-step guide.

First you will have to take a machine rental and purchase two chemicals: (One central heating inhibitor and one sludge remover)

  1. Drain a radiator: One in the bathroom is good as you will have water there and can drain the dirty water into the toilet. You may also have a bath to put the radiator in when it’s disconnected.
  1. Close the right and left radiator taps with some towels at the ready. Loosen but don’t disconnect one of the nuts that connects the radiator tap and the radiator. Have a flatish container ready for the water as it drains from the radiator (2-15min), the water may look very dark if the system is dirty.
  1. When all the water has been drained then you should disconnect the radiator taps, (right and left) from the radiator, carefully lifting it out. Connect the hoses from the machine directly to the 2 radiator taps (with supplied adaptors). Next open both valves on the radiator. Now you are in the system. The level of water may rise and might even overflow. Be ready. Now put the dump hose into the toilet, and tape it down.
  1. To fill the rental machine: put it in the shower tray or the bath, connecting the flow and put the dump hoses back according to instructions. Use the shower feed pipe, without the head, to fill the machine. Be careful not to overfill.
  1. Open the radiators right and left valves to the max, turned fully to the left.
  1. Start up the machine.
  1. Now start up the boiler – set the temperature at thirty degrees and programme on ‘constant’. The system should then heat up and the machine water will also heat up. (Some boilers won’t work when there is low pressure, so you may not be able to run your boiler while flushing.)
  1. Next add the chemical “sludge remover” while the machine runs according to the instruction – usually this will take around 2 hours. Do not leave the machine unattended.
  1. Isolate all but one radiator in the house. On all radiators, except the one to be cleaned first, turn off one valve – flow will be through this radiator. You can hammer the radiator gently with a rubber hammer to help sludge dislodge and then wait for five minutes before reversing the flow.
  1. Draining and filling: Ensure the dump hose is securely anchored in the toilet. Next you can discharge the dirty water from the radiator through the dump valve so that the dirty water flows into the toilet. The machine’s water level will drop so refill it every time water is dumped. Repeat these steps until the water is clear.
  1. Go to the next radiator and open the tap that is closed then close the one on the radiator that has just been flushed.
  1. To clean the radiator magnets, after each of the radiators has been cleaned, stop the machine then remove magnet or magnets and then wipe them clean. 
  1. Move through the system one after another reversing the flow and then dumping the water till it’s clean, cleaning the magnets as you go.
  1. Next the “inhibitor” chemical should be added to the machine and allowed to run for ten minutes.
  1. Now you can turn the machine off and close radiator taps in the bathroom disconnecting both the hoses and the machine.
  1. Wash the inside of the bathroom radiator (in the bath or shower cubicle) by filling it and then draining using the flexible shower hose utilised when you filled the machine. Once it is clean reconnect the radiator, open both of the taps and then bleed the air out.

At Grand Union Plumbing & Heating we are very proud of the high quality plumbing, heating and gas services that we offer. We are based in Milton Keynes, with many clients in the surrounding areas. Regardless of how complex or simple the job you need doing, you can rely on us, because we pride our selves on our customer service.  We are affordable and dependable, and we are ready to work with you on any project, large or small.

Any questions?

If you are looking for a heating engineer within the Milton Keynes area for anything from boiler installations to fixing a tap, or would like some friendly advice please call Mitch directly today on 01908 034194

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Areas we cover

  • Aylesbury
  • Bedford
  • Leighton Buzzard
  • Northampton
  • Olney
  • Towcester
  • Woburn Sands
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