Central heating power flushing explained
A power flush drives water and cleaning chemicals through your heating at high velocity to shift the black iron-oxide sludge that collects in radiators and pipework. It is the right fix for one specific problem and a poor fix for everything else. These eight guides cover both.
Start here
If you have not yet worked out whether you need one, that is the question that saves people the most money — a good share of people quoted for a flush have air in a radiator, a seized valve or an unbalanced circuit, all of which cost a fraction of the price.
Do I need a power flush? A straight checklist — three checks, about a minute, and most people stop at the second one.
Working out what is wrong
Sludge symptoms
What magnetite actually is, where it comes from, the symptoms that genuinely indicate it — and the six that people mistake for it.
Power flush vs chemical flush
Two different jobs at two different prices. On a lightly sludged system the £150 option may be all you need.
The disadvantages
Leak risk on old systems, a day of disruption, and the jobs a flush will never fix. The case against, in full.
The job itself
What it costs
£350–£800 by radiator count for 2026, why London runs higher, and every cheaper alternative listed above the expensive one.
How it's done
Step by step, including the radiator-by-radiator stage that takes the time and is the part most often skipped.
Is it worth it?
What genuinely improves on a sludged system, and an honest list of the seven things a flush will not fix.
Afterwards, and the bigger decisions
Magnetic filters & BS 7593
What stops the sludge coming back, what the British Standard requires with a new boiler, and why the filter must be emptied yearly.
New boiler or power flush?
When a flush is money spent twice, and what a boiler quote should itemise before you can compare it to another.
Heat pump cleanse
Heat pumps run lower flow temperatures with no output in reserve, so the cleansing standard is higher than for a boiler.
Also worth knowing
Commercial and multi-occupancy systems — offices, blocks, schools, care homes and pubs, where the building usually has to keep running while the work happens.
Power flushing FAQs — cost, timing, risk on older systems, landlord obligations and whether you can do it yourself.
Areas covered — around forty towns across London, Essex and Hertfordshire, each with what the local housing stock tends to mean for heating systems there.
Get an honest answer on what your system needs
Tell us the symptoms. We'll pass it to a Gas Safe engineer covering your area who can tell you whether you need a flush — including if the answer is no.