Repair or replace?
Rule of thumb: if your boiler is over 10 years old and the next repair quote is more than half the price of a new boiler, replacement usually wins on cost over a 5-year horizon. Modern boilers are 30%+ more efficient — the energy savings alone can pay back the install within 5–7 years.
1. Frequent breakdowns
A few boiler issues in a year is normal wear. Three or more callouts? You're into "throwing good money after bad" territory. Each repair gets you fewer months of life.
2. Constant pressure drops
If you're topping up the boiler pressure every week or two, there's a leak somewhere — and on older boilers, often a corroded heat exchanger. That's usually a major repair, not minor.
3. Banging, kettling, or whistling
Sludge and limescale buildup is reducing efficiency dramatically. Sometimes a power flush solves it. On a 12+ year old boiler, the flush often reveals the system is too far gone.
4. High gas bills
Modern A-rated boilers run at 90%+ efficiency. Old non-condensing boilers run at 60–70%. If your gas bill is much higher than neighbours with similar properties, your boiler is the likely culprit.
5. Boiler over 12 years old
Most boilers are designed for 10–15 years. After 12, parts become harder to source, manufacturer support drops, and warranties don't cover much. The next major fault often makes replacement the only sensible choice.
6. Black soot near the boiler
Soot or scorch marks around the boiler casing means incomplete combustion — produces carbon monoxide. This is a safety issue. Switch off, ventilate, and call a Gas Safe engineer immediately.
What to expect from a replacement
A like-for-like swap typically takes 1 day. A different location or upgrade (combi to system, system to combi) takes 2–3 days. Modern boilers come with 10–12 year manufacturer warranties when installed by an accredited engineer.