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A power flush in London costs £450 to £800 for most homes: about £450 to £620 for six radiators, £580 to £800 for eight and £700 to £950 for ten, which works out at £60 to £85 a radiator. A magnetic filter fitted at the same time adds £150 to £240, and central London quotes run 10 to 15 per cent higher.
| Job | London low | London typical | London high | UK typical | What moves the price |
|---|---|---|---|---|---|
| 6 radiators (flat) | £450 | £525 | £620 | £435 | Zones 1 and 2 add 10 to 15 per cent |
| 8 radiators (3-bed) | £580 | £680 | £800 | £495 | |
| 10 radiators | £700 | £800 | £950 | £535 | |
| 12 radiators | £850 | £1,000 | £1,200 | £600 | 14 radiators £1,000 to £1,450 |
| Chemical flush instead (light sludge) | £150 | £210 | £275 | £210 | Circulates cleaner for a day; no machine |
| Add-on: magnetic filter fitted | £150 | £200 | £240 | £220 | Protects a new boiler; MagnaClean or Fernox TF1 |
| Surcharge for a system or conventional boiler | £50 | £100 | £150 | Tanks and a cylinder mean more to flush |
A power flush pumps cleaning chemicals through the heating system at high flow, radiator by radiator, and drains the sludge and scale out until the water runs clear, then adds inhibitor. The signs you need one: radiators cold at the bottom and warm at the top, a boiler that bangs or kettles, rooms that take an hour to warm, black water when you bleed a radiator, or a pump that keeps failing.
It is also the job most new-boiler quotes hide in the small print. Manufacturers require the system to be cleaned and inhibited when the boiler is fitted, and the Benchmark checklist records it; skip it and a sludged system can void the warranty and kill the new heat exchanger within a few winters.
A chemical flush at £150 to £275 is the lighter option for a system with mild sludge: the cleaner circulates for a day and is drained. A power flush is the answer for real blockages and for anything over ten years old. London's hard water, at 250 to 350 milligrams of calcium per litre, scales systems faster than most of the country, and a quote well under £50 a radiator usually means a rushed job.
Prices last checked: September 2026. Based on the published 2026 per-radiator prices of two London firms and MyJobQuote's September 2026 guide. PROS AI does not yet have enough completed power flushes in London to publish its own averages.
£450 to £800 for most homes: six radiators £450 to £620, eight £580 to £800, ten £700 to £950, twelve £850 to £1,200. Per radiator that is £60 to £85. Nationally the average is about £550, and London's premium is labour plus 10 to 15 per cent more in Zones 1 and 2.
If the system has sludge, yes, and the installer will tell you after a look at the radiators and the old boiler's return. Manufacturers require the system to be flushed and inhibited at installation and record it on the Benchmark checklist; without it the warranty can be refused. A clean, young system may only need a chemical flush.
A chemical flush at £150 to £275 handles light sludge in a system under ten years old. A power flush at £450 and up moves ten times the water and clears blocked radiators and pipework. If a radiator is cold at the bottom, or you have had a pump or valve fail from debris, it is a power flush.
Radiators warm at the top and cold at the bottom, a boiler that kettles or bangs, slow warm-up, black or brown water from a bleed valve, or a heating engineer's report after a breakdown. A single cold radiator can just be air; bleed it first.
For sludge, yes, and the magnetic filter and inhibitor added at the end keep it that way for years. For a radiator that is cold because of a stuck valve, a failed pump or a design fault it does not; a good engineer checks those before quoting a flush.
Written by Shay Hazan, PROS AI.
£350 - £850per job
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