Deciding whether to replace an ageing boiler usually comes down to two separate questions: is it worth repairing at all, and if not, how quickly does a new one pay for itself. This calculator estimates your replacement cost by home size and shows the running-cost payback period based on your current boiler's age.
How this calculation works
Replacement cost is estimated from your home size using typical 2026 UK installer pricing for a like-for-like combi swap. Annual savings are estimated by applying a typical efficiency gain for a boiler of your current age, older boilers waste considerably more gas than a modern A-rated condensing unit, against your current annual gas bill. The payback period simply divides the replacement cost by that annual saving, showing how many years of lower bills it takes to recover what you spent.
Independent of the payback maths here, ongoing repair costs on an older boiler, heat exchangers, diverter valves, circuit boards, tend to add up faster than a straightforward one-off replacement once a boiler passes around 15 years old. See our Boiler Replacement Budgeting guide for the full repair-versus-replace reasoning.
Frequently asked questions
Does this calculator include heat pump options?
No, this specifically compares an old gas boiler against a new gas boiler. See our Heat Pump Payback Calculator for that separate comparison, including the Boiler Upgrade Scheme grant.
Why does a newer boiler still get some estimated savings in this tool?
Even boilers under 10 years old lose some efficiency over time through wear, scale build-up, and ageing components, so the savings estimate scales down but doesn't disappear entirely for a younger boiler. For a boiler under about 5 years old, the case for replacement on efficiency grounds alone is genuinely weak.
Is the replacement cost here accurate for a system or regular boiler, not just a combi?
This estimate assumes a like-for-like combi swap, the most common scenario. Converting from a system or regular boiler to a combi, or vice versa, typically costs more due to additional pipework, so treat this figure as a reasonable baseline rather than an exact quote for a conversion.
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