Repair or replace: the numbers
A like-for-like boiler replacement typically costs £1,800 to £3,500 installed, in quotes the online installer Heatable gave across 2,000 jobs from January to June 2026. A £450 repair is 13% to 25% of that. In a 3 bed semi with an old non-condensing boiler, where a new one would save about £190 to £350 a year, it equals 1.3 to 2.4 years of the saving.
| Repair quote | Share of a £1,800 to £3,500 replacement | Years of fuel saving it equals |
|---|---|---|
| £150 | 4% to 8% | 0.4 to 0.8 years |
| £300 | 9% to 17% | 0.9 to 1.6 years |
| £450 | 13% to 25% | 1.3 to 2.4 years |
| £600 | 17% to 33% | 1.7 to 3.2 years |
| £1,000 | 29% to 56% | 2.9 to 5.3 years |
| £1,800 | 51% to 100% | 5.1 to 9.5 years |
The data behind this table
The repair quote divided by Heatable's typical £1,800 to £3,500 for a like-for-like combi or system boiler swap, and by the Energy Saving Trust's £190 to £350 a year for a semi-detached house replacing an old gas boiler rated D to G. We found no published survey of repair prices that we could check, so the quotes in the table are examples, not typical prices.
A repair that costs as much as the low end of a replacement, £1,800, is the one clear case: price a replacement first. Below that, the repair is always the cheaper bill today, and the question is how long it will last, which no published figure answers.
What a new boiler would save
Replacing an old non-condensing gas boiler with an A-rated condensing one and new controls saves about £190 to £350 a year in a semi-detached house, according to the Energy Saving Trust, at July 2026 fuel prices. This is the saving you give up for every year you keep the old boiler running.
| Home | Old boiler rated D | Old boiler rated E | Old boiler rated F | Old boiler rated G |
|---|---|---|---|---|
| Detached house | £220 | £270 | £350 | £500 |
| Semi-detached house | £190 | £210 | £240 | £350 |
| Mid-terrace house | £140 | £160 | £180 | £270 |
| Detached bungalow | £170 | £190 | £220 | £320 |
| Flat, mid floor | £90 | £100 | £120 | £170 |
The data behind this table
Energy Saving Trust, for a gas home fitting an A-rated condensing boiler with a programmer, room thermostat and thermostatic radiator valves in place of an older boiler. D is 78 to 82% efficient, E 74 to 78%, F 70 to 74% and G under 70%. The Trust gives no end-terrace figure, so the calculator uses the semi-detached one, and none for oil or LPG.
If the boiler is already a condensing one, a new boiler saves far less: a measured median of 2.3% of gas use, about £20 a year in a typical 3 bed semi. On fuel alone a replacement would take 89 to over 100 years to pay back, so a condensing boiler is worth repairing unless the repair itself costs as much as a new one. The same figures drive our new boiler cost calculator.
How long a boiler lasts, and guarantees
A boiler should last up to around 15 years when it is regularly serviced and properly maintained, according to the boiler maker Viessmann. That is one manufacturer's statement, not a measured average, and we found no official figure. The calculator tells you where your boiler sits against it and draws no conclusion from age alone.
| Brand | Guarantee the maker states |
|---|---|
| Worcester Bosch | Up to 12 years |
| Vaillant | Up to 10 years |
| Viessmann | 7 years as standard on many boilers |
| Ideal | 2 to 12 years |
| Baxi | Up to 10 years |
The data behind this table
Each from the manufacturer's own website, read 5 October 2026. These are the guarantees each maker states, with conditions such as registration within 30 days, an approved installer and a service every year. See boiler prices by brand for the conditions.
If your boiler is younger than its guarantee, check the paperwork before paying for a repair: a fault with the boiler itself may be covered.
How the calculator works
Share of a replacement is your quote divided by Heatable's typical range for a like-for-like swap. Fuel saving is the Energy Saving Trust's range for your type of home if the boiler is non-condensing; for a condensing boiler of 10 years or more it is the DESNZ measured median applied to the gas an average home like yours uses, at the price cap of 7.97p per kWh; for a condensing boiler under 10 years old we have no sourced figure and count none. Years of saving is your quote divided by that saving, and payback is the replacement cost divided by it.
The verdict follows one rule: if the repair costs at least £1,800, the low end of a replacement, it says to price a replacement first. Otherwise it reports the figures and leaves the judgement to you. It does not estimate how long a repair will last, the chance of another fault, or a saving for oil or LPG, because we found no source for any of them.
Frequently asked questions
Is it worth repairing a 15 year old boiler?
On the figures, a £450 repair is 13% to 25% of a typical £1,800 to £3,500 replacement. If the boiler is an old non-condensing one in a semi, a new boiler would save about £190 to £350 a year, so the repair equals 1.3 to 2.4 years of that saving. Viessmann says a well maintained boiler should last up to around 15 years.
When is a boiler not worth repairing?
There is no official rule. Our calculator flags a repair that costs as much as the low end of a replacement, £1,800, and shows how many years of fuel saving the repair equals. How long the repair will last is the missing figure, and no source publishes it.
How long does a boiler last?
Up to around 15 years when it is regularly serviced and properly maintained, according to the boiler maker Viessmann. The longest manufacturer guarantees run to 12 years.
How much does a boiler repair cost?
We found no published repair price survey that we could check, which is why the calculator asks for your own quote and gives no typical repair price.
Does a new boiler save enough to justify replacing a working one?
Only if the old one is non-condensing. Replacing a condensing boiler saves a measured median of 2.3% of gas use, about £20 a year in a 3 bed semi, so a £1,800 to £3,500 replacement would take 89 to over 100 years to pay back on fuel alone.
Data sources
- Heatable, New boiler installation costs 2026 (updated 25 September 2026): typical installed prices from 2,000 of its own quotes, January to June 2026, its example estimates by home and its price ranges by brand. Heatable is an online boiler installer, so these are one firm's prices. Checked 5 October 2026.
- Energy Saving Trust, Boiler types explained (last updated 20 May 2026): yearly savings for a gas heated home fitting an A-rated condensing boiler with a programmer, room thermostat and thermostatic radiator valves in place of an older boiler, by the old boiler's rating, at July 2026 fuel prices; £3,500 typical cost of replacing a G-rated gas boiler. Checked 5 October 2026.
- Department for Energy Security and Net Zero, NEED impact of measures data tables 2026: the median fall in gas use in homes that had a new condensing boiler fitted, with and without new heating controls, priced at the Ofgem cap gas rate of 7.97p per kWh.
- Viessmann, What size of boiler do I need for my home? (22 March 2022): boiler size by radiators and bedrooms, the heat load of an average home, why an oversized boiler is not recommended, and that a regularly serviced boiler should last up to around 15 years. Read 5 October 2026.
- Guarantee lengths from each manufacturer's own site, read 5 October 2026: Worcester Bosch (Greenstar 8000+), Vaillant (ecoTEC exclusive), Viessmann (Viessmann warranty), Ideal (Ideal boiler warranties guide), Baxi (Baxi warranty registration).
- Department for Energy Security and Net Zero, Boiler Upgrade Scheme 2026 to 2030 summary business case, footnote 8: a new gas boiler costs about £3,500 including VAT. Other home sizes are scaled from it by our model, which is our assumption.
- Heat pump cost from our heat model, js/heat-model.js: the median installed price under the Boiler Upgrade Scheme for a heat pump of the size the home needs (DESNZ statistics, August 2026). EPC points from our EPC calculator model.