Central Heating Repair Cost Calculator
Cold radiators are usually air, sludge or a failed pump — three very different bills. Pick the symptom and this prices it.
Open the calculator →Price your heating fault in 30 seconds
4 steps. Covers the symptom, how much of the system is affected, urgency and region.
How this calculator works
Where a radiator is cold tells you most of what you need to know. Cold at the top is air — a bleed and rebalance, and the cheapest visit on this list. Cold at the bottom is sludge settling in the base, which a bleed will not touch; that needs a power flush. A radiator cold all over while others are hot usually points at the valve.
Scope matters because it changes the diagnosis, not just the labour. One cold radiator is local. The whole system cold points at the pump, the boiler or sludge throughout — which is why the calculator adds cost as the scope widens rather than treating it as the same job repeated. A quick read before you call helps: note which radiators are cold and where on each one, whether the boiler pressure sits in the green when cold, and whether the pump is warm and humming, because handing an engineer those three observations often turns a diagnostic visit into a fix on the first trip. Sludge is the thread running through most of these faults: it settles in radiator bottoms, drags on the pump and narrows the heat exchanger, and once a system is dirty enough the symptoms keep coming back until it is power-flushed and dosed with fresh inhibitor. A yearly service catches a lot of this before it turns into a repair — our boiler service cost calculator prices that — and if a tired boiler is the real weak link, the best boiler brands guide is worth a read before you spend on repeat repairs.
Central heating repair costs by job (2026)
| Repair | Typical 2026 cost | Notes |
|---|---|---|
| Bleed and rebalance system | £80–£150 | Air in the system |
| Radiator valve replacement | £100–£200 | Valve or TRV |
| Replace a radiator | £150–£400 | Corroded or holed |
| Circulating pump replacement | £250–£450 | Noisy or not circulating |
| Leak trace and repair | £150–£600 | Cost depends where it is |
| Power flush | £400–£800 | Sludge — radiators cold at the bottom |
| Out-of-hours call-out | +£80–£150 | Evenings, weekends, bank holidays |
Figures match our central heating repair guide. Any work on the gas side of the boiler must be done by a Gas Safe registered engineer — check the licence number on the Gas Safe Register yourself.
Heating repair calculator FAQs
Sludge. Magnetite and corrosion debris settle in the base of the radiator and block circulation there, so the top heats and the bottom stays cold. Bleeding will not help — that only releases air from the top. You need a power flush, and a magnetic filter afterwards to stop it returning.
If the system is genuinely sludged, yes — it restores output, cuts your gas use and protects the boiler. If a single radiator is affected, removing and flushing that one radiator is far cheaper. Ask the engineer to justify a whole-system flush before agreeing to it. Ask what chemicals and what flow rate they use as well, because a proper power flush moves water fast enough to lift settled magnetite, and a cut-price flush that is really just a chemical soak often leaves the sludge exactly where it was.
Usually a leaking radiator valve, a failed expansion vessel or a passing pressure relief valve. Worth fixing rather than topping up: every top-up introduces fresh oxygenated water, which accelerates corrosion and produces the sludge that causes the next problem.
Anything on the gas side of the boiler does, by law. Purely wet-side work — radiators, valves, pumps, flushing — can be done by a competent heating engineer or plumber. If in doubt, use a Gas Safe registered engineer and check the number on the register yourself. We do not verify that registration for you, so treat the card as a starting point rather than proof: the online register is the only place that confirms a licence is current and covers the specific gas work being done.
Related cost guides
- Heating repair cost guide — every fault priced
- Installation calculator — when a repair is not enough
- Boiler repair calculator — faults in the boiler itself
- Boiler servicing — catching faults before winter
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