Heating & Boilers
How Much Does a Power Flush Cost, and Do You Need One?
Published 1 September 2026 by WDI Group (Surrey) Ltd
A power flush is a deep clean of your central heating system. A pump is connected to the pipework and a chemical solution is circulated at high flow but low pressure to break up and remove the black iron oxide sludge that builds up inside radiators and pipework over the years.
UK prices typically range from around £400 to £800 depending on the size of the system. Our published rate is £550 excluding VAT for a power flush of up to ten radiators, with £40 per additional radiator, or £400 for a MagnaCleanse, which is a faster magnetic clean rather than a full flush.
It is also a job that gets sold when it isn't needed, so this guide covers how to judge whether your system genuinely warrants one.
Power flush prices
Our rate is £550 for a power flush covering up to ten radiators, and £40 for each radiator beyond that. A MagnaCleanse is £400 on the same radiator basis. If you do not already have a system filter fitted, one can be fitted alongside a MagnaCleanse from £150, which is what stops the sludge rebuilding as quickly afterwards.
All figures exclude VAT. A power flush is a fixed-price job rather than an hourly one because the time on site varies considerably with how badly contaminated the system turns out to be.
Signs your system may need flushing
- Radiators cold at the bottom but hot at the top, which is the classic sludge signature
- Some radiators never getting properly warm while others are fine
- Noisy pipework or a boiler that bangs, kettles or rumbles when it fires
- Cloudy, black or gritty water when you bleed a radiator
- The boiler repeatedly locking out or the pump failing more than once
- Heating that takes markedly longer to warm the house than it used to
Power flush or MagnaCleanse?
A power flush is the more thorough option. Water and cleaning chemicals are pushed through the system at high velocity in both directions, radiator by radiator, until the water runs clear. It takes several hours and is the right choice for a system with genuine, widespread sludge build-up.
A MagnaCleanse is a quicker magnetic clean that circulates the system through a powerful magnetic filter to capture iron oxide. It is less disruptive and less expensive at £400, and it suits systems that are moderately dirty or that are being cleaned as preventative maintenance rather than to fix a specific fault.
If you are unsure which you need, an engineer can take a sample of the system water and check radiators individually rather than guessing. We would rather sell you the £400 job that fits than the £550 one that doesn't.
When a flush is not the answer
Not every cold radiator is sludge. Trapped air, an unbalanced system, a stuck thermostatic valve, a failing pump or an incorrectly sized radiator all produce similar symptoms and none of them are fixed by flushing. Bleeding and balancing the system costs an hour of labour and should generally be ruled out first.
Be cautious of any quote for a power flush given over the phone without anyone having looked at the system, particularly if it arrives alongside a boiler replacement quote. A flush is a genuinely useful job on the right system and a waste of £550 on the wrong one.
Flushing before a new boiler
Most manufacturers require the system to be cleaned when a new boiler is installed, and many warranties depend on it along with a correctly fitted system filter. Fitting a new heat exchanger onto a system full of old sludge is the fastest way to block it.
If you are getting a replacement boiler quoted, check whether cleaning and a filter are included in the price or listed as extras, because that difference explains a lot of the variation between installation quotes.
How long it takes and what to expect
A power flush on an average three-bedroom house takes most of a working day. The engineer will need access to every radiator and to the boiler, and the heating will be off while the work is carried out.
Afterwards, the system is refilled with clean water and an inhibitor is added to slow future corrosion. Keeping that inhibitor topped up at each annual service, and having a system filter fitted, is what stops you needing the same job again in a few years.
Need help with this in your own home?
Cheam Plumbing is part of WDI Group (Surrey) Ltd. Call 020 3727 2578 and we will advise on availability and the quickest response we can provide, or view our published rates before booking.