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, the £50 still covers the engineer's home visit. All gas work is signed off by a Gas Safe registered engineer.
Talk to KJ about power flush
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