Boilers & Central Heating · Updated August 2026
Central Heating Repair Cost 2026
Most central heating repairs cost between £150 and £600, and the symptom usually tells you which end you are at. A radiator cold at the top is trapped air and often free to fix; cold at the bottom means sludge and points at a flush. Here are the 2026 ranges by job, what each symptom actually means, and how to judge a quote.
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How much does central heating repair cost?
Most central heating repairs fall between £150 and £600. The range is set by whether the fault is a single component, a system-wide problem such as sludge, or a leak that has to be traced before it can be fixed. These are ranges rather than prices — the diagnosis decides where you land.
| Job | Typical range | What moves it |
|---|---|---|
| Bleed & rebalance system | £80 – £150 | Number of radiators |
| Radiator valve replacement | £100 – £200 | Access, and whether the system must be drained |
| Replace a radiator | £150 – £400 | Size, type, and pipework changes |
| Circulating pump replacement | £250 – £450 | Pump spec and location |
| Leak trace & repair | £150 – £600 | Finding it is the variable, not fixing it |
| Power flush | £400 – £800 | Radiator count and how bad the sludge is |
These are ranges, not a quote — a heating engineer has to diagnose the fault first. Get my exact price →
Read your radiators: what the symptom tells you
Central heating faults announce themselves fairly clearly if you know what to look for. Working this out before you call saves diagnostic time — and lets you judge whether a quote makes sense.
| Symptom | Usual cause | Typical fix |
|---|---|---|
| Cold at the top, warm below | Trapped air | Bleed the radiator — often free |
| Cold at the bottom, warm above | Sludge and corrosion debris | Chemical or power flush |
| One radiator cold, rest fine | Stuck valve or airlock | Valve free-off or replacement |
| Upstairs hot, downstairs cold (or vice versa) | System out of balance, or failing pump | Rebalance, or pump replacement |
| Banging or kettling noises | Limescale or sludge in the boiler | Flush, and check water treatment |
| Pressure keeps dropping | Leak somewhere in the system | Leak trace — the cost variable |
Repair, flush, or replace the system?
- Repair when the fault is one component and the rest of the system is sound. Most call-outs are this.
- Flush when several radiators are cold at the bottom, the boiler is noisy, or you are fitting a new boiler to old pipework — many boiler warranties require the system to be cleaned first, and skipping it can void the cover.
- Replace the system when pipework is failing in multiple places, the system is microbore and repeatedly blocking, or you are already reconfiguring the house. Our central heating installation guide covers that job and its costs.
Getting a fair quote
- Insist on a diagnosis before a price — anyone quoting a power flush without seeing the radiators is guessing.
- Ask what happens if the flush does not fix it: a good engineer will tell you honestly when a system is beyond cleaning.
- Check the engineer is Gas Safe registered where any part of the work touches the boiler or gas supply.
- Get the parts and labour split, and any guarantee in writing.
- For anything over a few hundred pounds, get more than one quote on the same described fault — that is the only way the numbers are comparable.
Central heating repair FAQs
Most central heating repairs sit between £150 and £600. A single stuck radiator valve or a system that needs bleeding and rebalancing is at the cheap end; a failed pump, a leaking pipe under a floor, or a power flush to clear sludge moves toward the top. Where the fault is the boiler itself rather than the system around it, boiler repair pricing applies instead.
They are different faults, and the distinction matters. Cold at the TOP usually means trapped air — bleeding the radiator normally fixes it and costs nothing. Cold at the BOTTOM usually means sludge and corrosion debris settling inside, which points to a system needing a chemical flush or power flush. If most radiators are cold at the bottom, treat it as a system problem rather than a radiator problem.
A power flush pumps water and cleaning chemicals through the system at high velocity to clear sludge and corrosion. It typically costs £400–£800 depending on the number of radiators. It is worth doing when radiators are cold at the bottom, the boiler is noisy or repeatedly cutting out, or before fitting a new boiler onto an old system — many manufacturers require it for warranty.
Simple faults — bleeding, valve replacement, thermostat swaps — are usually a single visit of one to three hours. A power flush takes most of a day. Tracing a leak under floors or in walls is the unpredictable one: the finding can take longer than the fixing.
Support varies and changes, so check current eligibility rather than relying on older advice. Start with the government's own pages on home heating help at gov.uk, and your energy supplier's Priority Services Register, which can also bring practical help during a breakdown.
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Reviewed by the BestBuilders editorial team on 8 August 2026 · Price ranges from the BestBuilders 2026 Cost Index (live quote data, 519 UK towns) · Next scheduled review: November 2026 · See our editorial standards.