For a typical semi-detached home, repairing a boiler under 8 years old is worth it if the repair costs less than about £1,780. That falls to about £840 at 8 to 12 years and £310 at 12 to 15 years. Once a boiler is 15 to 20 years old, replacing it usually costs less over time than any repair.
Work it out for your boiler
Our verdict
Close call
Over the next 4 years, about how long a boiler 12 to 15 years old usually has left, the two options come out within about £40 of each other. Choose on budget, and on how much a winter without breakdowns is worth to you.
Repairing this boiler makes sense if the repair costs less than about £310.
| If you repair | |
|---|---|
| The repair | £350 |
| Likely further repairs (£100 a year) | £400 |
| Extra gas an older boiler burns (£65 a year) | £260 |
| Total | £1,010 |
| If you replace now | |
| A new boiler, its cost spread over its life (£245 a year) | £970 |
Based on a semi-detached house, a boiler 12 to 15 years old, a £350 repair and a £2,500 new boiler, with gas at 7.97p per kWh.
- This compares long-run cost, not cash today. If paying for a new boiler now would be a stretch, a repair can buy time. Finance costs are not included.
The most a repair is worth, by boiler age
If a repair costs more than the figure below, replacing the boiler is likely to work out cheaper over the years it has left. Assumes no breakdowns in the last two years, a £2,500 new boiler and gas at 7.97p per kWh.
| Boiler age | Flat | Mid-terrace | Semi-detached | Bungalow | Detached |
|---|---|---|---|---|---|
| Under 8 years | £1,880 | £1,810 | £1,780 | £1,800 | £1,670 |
| 8 to 12 years | £990 | £890 | £840 | £870 | £700 |
| 12 to 15 years | £470 | £360 | £310 | £340 | £170 |
| 15 to 20 years | £170 | £30 | Replace | Replace | Replace |
| Over 20 years | Replace | Replace | Replace | Replace | Replace |
"Replace" means the extra gas and likely further repairs outweigh the value left in the old boiler, so even a cheap repair tends to cost more over time.
How the calculator works
Repairing keeps your old boiler for the years it probably has left. Over those years you pay for the repair, for any further repairs, and for the extra gas an older, less efficient boiler burns. Replacing now means paying for a new boiler sooner. Its yearly cost is its price spread over its lifespan, plus a small allowance for the cost of paying earlier. The calculator compares the two over the years the old boiler has left.
A repair is worth it when it costs less than: years left × (yearly cost of a new boiler − likely repairs a year − extra gas a year).
Assumptions
| Assumption | Value | Basis |
|---|---|---|
| Gas price | 7.97p per kWh | Ofgem price cap, 1 October to 31 December 2026 (average Direct Debit rate) |
| New boiler efficiency in use | 90% | A-rated condensing boiler with modern controls. EnergyGuide estimate. |
| New boiler lifespan | 12.5 years | Midpoint of the Energy Saving Trust's 10 to 15 years. |
| Cost of money | 3% a year above inflation | Replacing early means paying sooner, which costs interest you could have earned or paid on a loan. EnergyGuide estimate. |
| New boiler price | £2,500 | Typical like-for-like combi swap. Replace it with your own quote. |
| Heat each home needs a year |
Flat: 4,150 kWh Mid-terrace house: 8,500 kWh Semi-detached house: 10,200 kWh Bungalow: 9,100 kWh Detached house: 16,000 kWh |
Set so a G-rated to A-rated upgrade reproduces the Energy Saving Trust's July 2026 savings for flats, semis and detached homes. Terrace and bungalow follow the Trust's earlier ratios. |
By boiler age
| Boiler age | Efficiency | Years left | Repairs a year |
|---|---|---|---|
| Under 8 years | 88% | 9 | £25 |
| 8 to 12 years | 86% | 6 | £60 |
| 12 to 15 years | 84% | 4 | £100 |
| 15 to 20 years | 80% | 3 | £140 |
| Over 20 years | 68% | 2 | £180 |
These age figures are EnergyGuide estimates, not published statistics. A boiler that has broken down in the last two years gets a higher repair allowance: once 1.5×, twice or more 2.5×. Have better data? Tell us.
Sources
- Ofgem: energy price cap, 1 October to 31 December 2026
- Ofgem: energy price cap, 1 July to 30 September 2026 (used to calibrate heat demand)
- Energy Saving Trust: boiler lifespan and upgrade savings
- Centre for Sustainable Energy: Energy Saving Trust saving for a semi-detached home, July 2026
- Worcester Bosch: Energy Saving Trust saving for a detached home, July 2026
- MoneySuperMarket: Energy Saving Trust savings by home type
Repair or replace: common questions
Is it worth repairing a 15-year-old boiler?
Usually not. For a typical semi-detached home, a boiler 15 to 20 years old has about 3 years left and burns about £115 a year more gas than a new one, so even a cheap repair tends to cost more over time than replacing. A small repair can still make sense to get you through a winter while you save or compare quotes.
When is a boiler not worth repairing?
When the repair costs more than the break-even for its age. For a typical semi-detached home that is about £310 for a boiler 12 to 15 years old. Other signs point the same way: the boiler is over 15 years old, parts are hard to get, it has broken down more than once in two years, or your gas bills have crept up without a change in use.
How long does a boiler last?
Usually 10 to 15 years, according to the Energy Saving Trust. Many last longer with annual servicing, but efficiency and reliability fall with age. This calculator assumes a repaired boiler has about 9 more years if it is under 8 years old, falling to about 2 once it is over 20 years old.
How much could a new boiler save on my gas bill?
The Energy Saving Trust estimates that replacing an old G-rated boiler with an A-rated one and full heating controls saves about £130 a year in a flat, £320 in a semi-detached house and £500 in a detached house, at July 2026 prices. At 7.97p per kWh, this calculator puts the saving for a semi-detached home with a boiler over 20 years old at about £290 a year.
My engineer says my boiler is condemned. What does that mean?
Gas engineers classify unsafe appliances under the Gas Industry Unsafe Situations Procedure. "Immediately Dangerous" means the boiler must stay off until it is put right. "At Risk" means a fault could become dangerous, so the engineer will advise against using it and ask to disconnect it (Gas Safe Register). Either can often be fixed with a repair, so ask for the classification and the fix in writing, then compare that price with the break-even above.
Should I pay for a repair if my boiler is under warranty?
Check the manufacturer's warranty first. Many boilers fitted in the last decade carry warranties of 7 to 12 years, usually on condition that the boiler has been serviced every year. A covered repair costs you nothing, which makes repairing the clear choice.
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