Boilers & Heating
Power flush
TL;DR
A proper power flush on an 8-radiator home takes 4-6 hours and costs £450-£650. It's worth doing when: radiators have cold spots at the bottom, the boiler is short-cycling or making kettling noises, or you're fitting a new boiler onto an old system (Worcester and Vaillant both make it a warranty condition). It's not worth doing on a system that's just noisy from air.
A power flush is not a magic fix — it's a mechanical cleanse of a heating system that's silted up with black magnetite sludge, limescale and copper debris. Done properly with a jet-pump and the right chemicals, it restores full flow through every radiator, prevents boiler component damage, and is a common warranty condition when a new boiler is fitted to an existing system.
This page covers what a proper power flush looks like, when it's genuinely needed, when it isn't, and what a fair fitted price is in 2026.
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When do you actually need a power flush?
Three genuine reasons: cold spots at the bottom of radiators (classic sludge signature), boiler short-cycling or making kettling / rumbling noises, or a new boiler installation on an existing system where the manufacturer requires proof of clean water for the warranty. If your issue is trapped air, one noisy pump, or a single cold radiator — a power flush is overkill and we'll say so.
- Cold patches at the bottom of one or more radiators
- Boiler kettling, banging or short-cycling
- Radiators slow to warm up compared to others near the boiler
- System water is thick, black and inky when bled
- New boiler being fitted — Worcester, Vaillant, Ideal, Baxi all require flush + filter
What does a proper power flush include?
We connect a jet-pump machine (Kamco CF210, MagnaCleanse or equivalent) either to the pump position or across a radiator tail. The pump then circulates the whole system through a magnetic capture chamber at 100+ litres per minute, forward and reverse. We add a heavy-dose descaler and sludge remover, isolate each radiator in turn to blast localised debris, then neutralise, flush clean, and refill with fresh water and BS 7593 compliant inhibitor.
- Rated jet-pump connected in the correct position for flow
- Fernox F3 or Sentinel X400 chemical cleanser dosed
- Individual radiator isolation and reverse-flush — every rad, every direction
- Full system neutralise until running clean at the drain
- Refill and inhibitor to BS 7593:2019 (Fernox F1 or Sentinel X100)
- MagnaClean or Adey filter fitted where none exists
- Written report with before/after water clarity photos
How long does a power flush take?
8-radiator home: 4-6 hours on site. 10-12 radiators: 6-8 hours. Very silted systems or larger properties can be a full day. We don't 'quick flush' in 90 minutes — that's a chemical rinse, not a power flush, and it won't hit the warranty threshold on a new boiler install.
Power flush vs chemical clean vs MagnaCleanse?
A chemical clean (Fernox / Sentinel dosed into the system and left circulating for 7-14 days) is fine for prevention. A MagnaCleanse (Adey's rapid magnetic flush kit) is a middle-ground for moderately dirty systems — about 90 minutes on site. A full power flush with a jet-pump is what you need for badly silted systems or new boiler warranty compliance. We'll always recommend the least invasive option that solves your actual problem.
Will a power flush damage old radiators or joints?
Very old radiators (30+ years) with corroded joints are the one risk. The high-flow of a power flush can expose leaks that were being held together by sludge. We do a full visual inspection first and warn you if any joints look marginal — sometimes it's better to replace one or two rads before we flush, rather than after.
Typical prices
Real-world ranges from recent Northwest jobs. Your final price is confirmed in writing before any work starts.
| Item | Typical price | Notes |
|---|---|---|
| Power flush — up to 8 radiators | 450 – 650 | 4-6 hours on site |
| Power flush — 9 to 12 radiators | 650 – 850 | 6-8 hours on site |
| Power flush — 13+ radiators / large property | 850 – 1,200 | Full-day job |
| MagnaCleanse rapid flush (moderate silt) | 280 – 380 | 90-120 minutes, mid-tier option |
| Chemical inhibitor cleanse (mild systems) | 150 – 220 | Dosed, left 7-14 days, then drained |
| MagnaClean Pro 2 filter — supplied & fitted | 180 – 260 | Fitted at the same time |
| Radiator replacement (per rad, if needed) | 180 – 280 | Old rad flagged during survey |
| Full written before/after report | included | Photos + inhibitor concentration |
Which brand should you fit?
We flush using Kamco and Adey MagnaCleanse jet-pump equipment, and we dose with Fernox F3 (cleanse) and F1 (inhibitor) or Sentinel X400/X100 — the industry-standard chemicals accepted by every UK boiler manufacturer's warranty. We install and service Worcester Bosch, Vaillant, Ideal, Baxi, Viessmann and Alpha — none of them pay us commission and we don't push a "boiler of the month".
Our promise on this job
Flat £50 diagnostic — deducted in full from any work booked. Fair, transparent quote before we start. If we can't fix the fault we diagnosed, we refund the diagnostic. All gas work is signed off by a Gas Safe registered engineer.
Talk to KJ about power flush
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