Decision tool / May 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
GBP 100-GBP 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
GBP 1,800-GBP 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)
GBP 2,500-GBP 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
GBP 8,000-GBP 14,000
Air source heat pump (after GBP 7,500 BUS grant typically GBP 500-GBP 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 | GBP 100 - GBP 180 | 5+ years (often a simple replacement) |
| Expansion vessel | GBP 150 - GBP 280 | 5-10 years (or original boiler lifespan if external) |
| Diverter valve | GBP 220 - GBP 350 | 5-8 years |
| Fan or pump | GBP 200 - GBP 400 | 5-8 years |
| PCB / control board | GBP 300 - GBP 500 | 5-10 years (often the same age as the boiler) |
| Gas valve | GBP 350 - GBP 550 | 10+ years |
| Heat exchanger | GBP 500 - GBP 900 | If primary fails on a 10+ year boiler, replacement is often better value |
| Diagnostic call-out only | GBP 80 - GBP 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 GBP 700-GBP 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 GBP 200-GBP 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 GBP 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 GBP 1,400 per year, that's GBP 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 GBP 800 repair on a 13-year-old boiler with an estimated 2-3 years of life left compares poorly with a GBP 2,500 replacement that comes with a 12-year warranty and saves GBP 250-GBP 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 GBP 100-GBP 180, diverter valve GBP 220-GBP 350, PCB GBP 300-GBP 500, heat exchanger GBP 500-GBP 900. Call-out diagnostic alone GBP 80-GBP 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 GBP 7-GBP 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.