Decision tool / June 2026
Should I repair or replace my boiler?
The 50% rule is the headline answer: a repair is cost-justified up to roughly 50% of a like-for-like replacement. The complete answer also folds in boiler age, breakdown frequency, and the annual gas-saving of moving from your current ErP band to an A-rated condensing boiler.
The four options on the table
Repair
£100-£900
Single-fault fix on the existing boiler. PCB swap, pump replacement, diverter valve, or heat exchanger.
Best when
Boiler under 10 years old, first major fault, repair cost under 50% of a swap.
More on this option →Like-for-like swap
£1,800-£4,500
Same fuel, same boiler type. The cheapest replacement path. 1-day install on most homes.
Best when
Boiler over 12 years old, breakdowns getting frequent, no need to change fuel or layout.
More on this option →Convert (e.g. back boiler to combi)
£2,500-£5,000
New pipework + flue + decommission existing setup. Back boiler conversion, regular-to-combi, system-to-combi.
Best when
Awkward layout in current system, wanting to free up loft tank space, modernising heating.
More on this option →Heat pump alternative
£8,000-£14,000
Air source heat pump (after £7,500 BUS grant typically £500-£6,500 net). No gas at all.
Best when
Well-insulated home, EPC C+ ideally, room for an outdoor unit, comfortable with a 4-6 week lead time.
More on this option →Common UK repair costs
Typical UK 2026 Gas Safe engineer call-out plus part fitted. Labour usually covered within a 1-hour call-out for simple parts; complex jobs (heat exchanger, full burner) run to a half-day plus.
| Repair | Typical cost | How long it usually lasts |
|---|---|---|
| Pressure sensor | £100 - £180 | 5+ years (often a simple replacement) |
| Expansion vessel | £150 - £280 | 5-10 years (or original boiler lifespan if external) |
| Diverter valve | £220 - £350 | 5-8 years |
| Fan or pump | £200 - £400 | 5-8 years |
| PCB / control board | £300 - £500 | 5-10 years (often the same age as the boiler) |
| Gas valve | £350 - £550 | 10+ years |
| Heat exchanger | £500 - £900 | If primary fails on a 10+ year boiler, replacement is often better value |
| Diagnostic call-out only | £80 - £150 | n/a |
Decision flow by boiler age
Under 7 years old
Repair, almost always. The boiler likely still has warranty cover - check with the manufacturer first, even an out-of-warranty fault on a near-new boiler is rarely worth replacement.
7 to 12 years old
Repair if the cost is under 30-40% of a replacement (under £700-£800). Replace if you've had two or more callouts in the past 12 months, or the boiler is rated D or below on the ErP scale - the annual gas saving on a modern A-rated boiler pays back the install in 4-7 years.
12 to 15 years old
Replacement is usually the better whole-cost-of-ownership play. Boilers this old typically run at 70-82% efficiency vs 92-94% on an A-rated modern condensing boiler. Energy Saving Trust calculates a typical UK household saves £200-£580/year on gas bills replacing a G-rated boiler with an A-rated equivalent.
Over 15 years old
Repair only if the fault is trivial (under £200). Parts availability starts to decline meaningfully past 15 years. Major component failures (heat exchanger, gas valve) on a 15+ year boiler are almost always a flag to replace rather than nurse another year.
The 50% rule explained
The rule of thumb works because of three compounding effects on an older boiler:
- Future repair frequency. A first fault on an older boiler rarely stays the only one. Bayesian read: the next 12 months are 2-3x more likely to bring another callout once the first major repair is done.
- Efficiency gap. A 15-year-old boiler at 75% efficiency vs a new A-rated boiler at 93% means roughly 18 percentage points of gas wasted. On a typical UK household gas bill of £1,400 per year, that's £250 annual waste compounding for the remaining life of the old boiler.
- Warranty reset. A new boiler typically comes with a 10-12 year warranty, eliminating the breakdown call-out risk entirely for over a decade.
Put together: a £800 repair on a 13-year-old boiler with an estimated 2-3 years of life left compares poorly with a £2,500 replacement that comes with a 12-year warranty and saves £250-£400 per year on gas. The replacement pays back in 5-7 years and runs problem-free for the next 12.
FAQ
When is a repair worth it vs replacement?
Roughly 50% of replacement cost is the break-even. Under 7 years old, almost always repair. Over 12 years, replacement is usually the whole-cost winner.
How much do common UK boiler repairs cost in 2026?
Pressure sensor £100-£180, diverter valve £220-£350, PCB £300-£500, heat exchanger £500-£900. Call-out diagnostic alone £80-£150.
How long do modern UK boilers last?
12-15 years typical, up to 20+ with regular servicing. Efficiency declines meaningfully after 10-12 years even on well-maintained units.
If I repair, will the rest of the boiler fail soon?
Likely. The base-rate finding is that the year after a first major repair sees 2-3x more callouts than a year without one. The expected-cost over the next 3 years often flips the repair-vs-replace decision toward replacement.
Should I get a service plan instead?
A boiler cover plan (British Gas, HomeServe, CheckaTrade) is typically £7-£25 per month covering repairs + annual service. Useful for older boilers where breakdown risk is high but replacement isn't yet justified. See sister site boilerservicecost.com for a comparison.
Decided to replace? See cost by boiler type then cost by brand. Cover plans more your speed? boilerservicecost.com.