For most homes, a thorough power flush takes most of a working day. The exact time depends on the size of the system and how contaminated it is.
Typical timings
| Property | Typical radiators | Typical time on site |
|---|---|---|
| Flat or small house | Up to 6 | Around half a day to a day |
| Medium house | 7–10 | A full working day |
| Larger house | 11–15 | A long day, sometimes more |
| Large or complex system | 16+ | Can run into a second day |
These are general guides, not guarantees. We’ll give you a realistic estimate for your own home when we quote.
What makes a power flush take longer?
- More radiators. Each one is flushed individually, so time scales with radiator count.
- Heavy sludge. Badly contaminated radiators need longer agitation and more flushing to waste.
- Seized valves. Radiator valves that won’t close have to be dealt with before the radiator can be isolated.
- Microbore pipework. Needs a more careful approach to avoid blockages.
- Access. Distance to a suitable drain, radiators behind furniture, boilers in awkward cupboards.
- Scale. A descaling stage adds circulation time.
Why you shouldn’t rush it
The part of a power flush that takes the longest — isolating and flushing each radiator in turn — is the part that actually clears blocked radiators. A flush that skips it will leave the worst radiators untouched. It’s worth asking any engineer how they’ll flush each radiator; see how a power flush works.
How to prepare
- Clear space around the boiler and each radiator
- Let us know about radiators behind fitted furniture or boxing
- Plan for no heating and hot water for most of the day
- Make sure someone is available at the start and end
A typical day, hour by hour
Every job differs, but on an average three-bedroom house with around nine radiators, the day often looks like this:
- Arrival and system check — looking at the boiler, radiators and valves, testing the water and agreeing the plan with you.
- Set-up — dust sheets down, the flushing machine connected and the dump hose run to a suitable drain.
- Chemical circulation — the cleaner is circulated around the whole system to start loosening deposits.
- Radiator-by-radiator flushing — the longest stage, working through each radiator in turn with flow reversal and agitation, then dumping to waste until clear.
- Final flush and testing — checking water quality against the mains supply.
- Refill, inhibitor and recommission — the pump refitted, system refilled and bled, inhibitor added, and the boiler run up to check every radiator heats evenly.
Can the heating be used the same evening?
Yes. Once the system is recommissioned, the heating and hot water work as normal. Radiators may need bleeding again over the following days as any remaining air works its way out — we’ll show you how, and on sealed systems explain what pressure to look for on the gauge.
Adding a magnetic filter on the day
If you choose to have a magnetic filter fitted, it’s usually installed during the same visit, adding a little time to the day. It’s best fitted while the system is drained anyway.
For pricing, see power flush cost in London.