Last Updated on August 12, 2026
The power flush is the most quietly upsold job in heating. Sometimes it is exactly what a sludged system needs. Sometimes it is £600 added to a boiler quote out of habit. Here is how to tell the difference.
The mistake: buying a flush without a reason
Cold spots at the bottom of radiators, dirty black water when bleeding, kettling noises, repeated pump failures: those are reasons. “We always do one” is not. Ask what was found, and ask whether a cheaper chemical clean would do.
What a power flush costs in 2026
| Property size | Typical cost |
|---|---|
| 2-bed flat, around 4 radiators | £350 |
| 2-bed house, around 6 radiators | £450 |
| 3-bed house, around 10 radiators | £550 |
| 4-bed house, around 15 radiators | £800 |
Secondary guides price per radiator at roughly £80 to £120. Done as part of a boiler installation, a flush is often bundled nearer £1,000 including VAT, which is worth negotiating.
What you should get for the money
A proper flush takes several hours, uses a flushing unit and chemicals, and ends with an inhibitor added and, ideally, a magnetic filter fitted. Before and after evidence is reasonable to ask for: temperature readings or water samples. A flush quoted at an hour of work is not a flush.
New boiler manufacturers commonly require system cleaning for the guarantee to hold, which is why it appears on installation quotes. That is legitimate. Paying full standalone price inside a £3,000 install is not, so query the line item.
The checks
A flush on its own is not gas work, so no licence applies, which means the usual rule: check the firm, not the claim. Established company, real reviews, willing to explain why the system needs it. If the flush comes bundled with a boiler, the installer must be Gas Safe registered for the boiler itself, and you can check the number.
The sharp takeaway
A power flush is a repair, not a ritual. Ask for the symptom that justifies it, expect £350 to £800 by house size, and get the inhibitor and filter included in the price. If nobody can tell you why your system needs one, it probably does not.
Part of our plumber cost series. See also new boiler cost.
