The key variables
The repair-vs-replace decision comes down to three factors: the age of the boiler, the cost of the repair, and the efficiency of the existing boiler vs a replacement. Here's a structured way to think through it.
The 50% rule
A useful rule of thumb: if the repair cost exceeds 50% of what a replacement boiler would cost, replace the boiler. Paying £600 to repair a boiler when a new one (with 10-year warranty) costs £1,099 is poor value — especially if the boiler is likely to develop further faults.
Age of boiler
- Under 5 years: almost always worth repairing — the boiler has most of its life ahead of it
- 5–8 years: repair if cost is under £300
- 8–12 years: repair only if under £200 and no other recent faults
- Over 12 years: seriously consider replacement regardless of repair cost — efficiency loss and increasing failure frequency make this the better long-term choice
Efficiency savings from replacement
An old boiler running at 70% efficiency vs a new 94% efficiency boiler: saving approximately 24% of your gas bill. On a £1,200/year gas bill, that's £288/year. A new boiler at £1,099 pays back in under 4 years in energy savings alone.
Common expensive repairs
Heat exchanger replacement: £400–£700. PCB replacement: £300–£500. Gas valve: £200–£350. Secondary heat exchanger: £250–£400. Any of these on a boiler over 10 years old: strong case for replacement.
The warranty advantage
A new boiler comes with 5–12 years manufacturer warranty, covering parts and labour. Repairing an old boiler gives no such protection — the next fault is yours to pay for.
Verdict
Simple fault on a boiler under 8 years old: repair. Expensive repair (£400+) on any boiler over 10 years old: replace. Always under 12 years: consider whether the repair is a precursor to more failures. We'll always give you an honest assessment on the same visit as the diagnostic.