Common faults and 2026 prices
Diverter valve replacement: £180–£320 fitted. Causes: hot water but no heating, or vice versa.
Expansion vessel re-pressurise / replace: £120–£260. Causes: pressure dropping repeatedly.
PCB (printed circuit board): £280–£550. Causes: random fault codes, won't fire, intermittent.
Pump replacement: £220–£380. Causes: noisy boiler, no circulation.
Heat exchanger replacement: £450–£900. Causes: leaking from inside the case, persistent error code. At this price, on a boiler over 8 years old, replace the whole boiler instead.
When to repair, when to replace
Repair makes sense if: the boiler is under 7 years old, the repair is under 30% of a new boiler's installed price, and the unit isn't on the manufacturer's discontinued list (parts get expensive when discontinued).
Replace if: the boiler is over 10 years old, the repair quote is over £450, you've had two unrelated faults in 18 months, or the model is obsolete. A new mid-range A-rated combi installed runs £2,500–£3,200 in our region.
Avoiding repeat callouts
Most repeat boiler issues trace to system water quality. A magnetic filter (around £180 fitted) catches the iron oxide that destroys pumps and PCBs, and a good chemical inhibitor keeps things flowing. Every boiler service should include checking inhibitor levels — if yours doesn't, ask why.