BoilerFaultCodesWhen to replace your boiler: 7 signs it's time
A repair can keep an old boiler limping for another year, but at some point the maths stops working. Here's how to tell when you've crossed that line — and a simple calculation for whether replacement actually saves you money in your specific case.
The £1,000 rule
If you'd spend more than £1,000 on repairs in one year, a new boiler is usually the right call. A mid-range combi installs for £2,000–£3,500; 0% finance is widely available; and the fuel saving alone typically covers £300–£500 of the payments each year on an old G-rated boiler.
The 7 signs
It's over 10 years old
Average UK boiler life is 10–15 years. At 10+, parts get harder to source and efficiency drops below modern A-rated models. Reliability falls off a cliff at around 12–15 years.
You've called the engineer 2+ times this year
Rule of thumb: if repair bills in 2 years exceed half the cost of a new boiler, replace it. A typical diverter valve (£300) + PCB (£400) + pump (£250) in one winter is £950 — and you still have an old boiler.
Energy bills are climbing
A G-rated (pre-2005) boiler runs at ~70% efficiency. A modern A-rated boiler runs at 92–94%. On a £2,000-a-year heating bill, that difference is £400–£500 a year.
It's making new noises
Banging, kettling, humming are signs of limescale, sludge, or failing pump — repair is possible but often buys you only 1–2 more years.
Parts are hard to find
Discontinued boilers (Potterton Suprima, Worcester CDi, Vaillant Turbomax, Baxi Solo) — engineers can still fit parts but they're slower to source and more expensive.
Leaks — from the boiler itself
Small weeps from pipes are usually repairable. Water from the casing, boiler body, or heat exchanger is almost always terminal — heat exchanger replacement costs more than most people spend on a new boiler.
Yellow/orange flame or CO concerns
If your boiler has ever shown a yellow flame or triggered a CO alarm, replace it. Some repairs are possible but the safety margin is not worth the saving.
The repair-or-replace calculation
Simple payback test — takes 30 seconds:
Or the short version: if repair is more than 40% of the new-boiler cost and your boiler is over 8 years old, replace.