Is it worth servicing again, or is it time to replace?

An annual service typically costs £80–£120 (Which?, 2026) and is the cheapest way to keep a boiler running safely and efficiently: it catches small faults, like a failing pump seal or a dirty heat exchanger, before they turn into a breakdown. The rule most heating engineers work to is that once a boiler passes 10–12 years old, and a single repair quote comes in above roughly 30–40% of the cost of a new one, replacement usually makes more financial sense than another patch repair, because parts for older models get harder to source and efficiency keeps dropping.

Say your 13-year-old boiler needs a £320 repair. That's over a third of what a straightforward combi replacement at the lower end of the £2,000–£3,500 range (Which?/HomeOwners Alliance, 2026) would cost. You'd still own a 13-year-old boiler afterwards, too, with no warranty and no efficiency improvement.

If you're weighing up a repair bill against a replacement quote, run both figures through the calculator before you agree to anything: a repair that looks cheap in isolation can turn out to be the expensive option once you compare it against a new boiler with a 10-year warranty.

Combi, system or regular: why does the type change the price?

The three boiler types aren't interchangeable, and pricing reflects that. A combi boiler heats water on demand straight from the mains, with no tank or cylinder needed. It's the most common choice in UK homes, usually the cheapest and quickest to install, which is why it sits at the lower end of the £2,000–£3,500 replacement range. A system boiler uses a hot water cylinder and suits homes with more than one bathroom or higher simultaneous demand, so it tends to cost more because of the extra cylinder and pipework. A regular (conventional) boiler keeps both a cylinder and a cold water tank, typically in the loft, and is usually only fitted when replacing an existing regular system like-for-like, since converting to a combi adds substantial extra labour.

Swap a like-for-like regular boiler for a combi and you pay to remove a tank, cap off pipework, and sometimes upgrade the mains pressure, on top of the boiler itself. That's why two quotes for what looks like the same job can be £1,000 or more apart.

Before you compare quotes, check whether each engineer is pricing a like-for-like swap or a conversion to a different boiler type, because that difference (not the boiler brand) usually explains the biggest gap between two prices.

Should you pay upfront or finance the replacement?

Paying upfront avoids interest altogether, but £2,750 is a lot to find in one go, and plenty of homeowners spread the cost over a personal loan instead. The trade-off is straightforward: financing turns a one-off bill into a smaller monthly payment, but you pay for that convenience through interest, so the total cost ends up higher than the cash price.

Worked example: £2,750 replacement, 3-year term, 7.9% representative APR

Paid upfront: £2,750, no interest.
Financed over 3 years at 7.9% APR: roughly £86 a month, £3,096 total (around £346 more than paying cash), in exchange for spreading the cost.

If you've got £2,750 sitting in savings earning less than 7.9%, the maths points toward paying upfront and keeping finance for situations where the cash genuinely isn't there. Try the improvement loan calculator to see how the numbers shift over a 5-year term instead of 3.

How do you get a genuine like-for-like quote?

Boiler quotes vary enormously by property type, boiler brand and how difficult access is. Moving a boiler's location, rerouting a flue, or fitting one into a tight loft space can add hundreds of pounds before you've even chosen a brand. That's why the figures in this calculator are a planning tool, not a quote: always get at least two like-for-like quotes from Gas Safe registered engineers before committing, and make sure both are pricing the same boiler type, output size and warranty length.

A quote that's a few hundred pounds cheaper than another is worth a second look: check whether it includes a full system flush, a matching warranty and the same brand tier. A cheaper like-for-like quote is a genuine saving; a cheaper quote for a lower-spec boiler isn't a saving at all.

Two quotes that look close on price but cover different work aren't actually comparable, so ask each engineer to itemise exactly what's included before deciding which one is genuinely the better deal.

What this means for you

Most people who run these numbers end up doing one of two things: repairing a boiler under about 8 years old with a straightforward, affordable fault, or replacing anything over 12 years old once a repair quote pushes past a third of the replacement cost. If you're in the position of choosing between financing and paying upfront, the example above holds broadly true across terms. Financing at 7.9% APR typically adds 10–13% to the total cost of a mid-range combi replacement, so it's worth checking your savings rate before assuming finance is the easier option.

Keep track of what you spend on the boiler, and everything else the property needs, using the cost of ownership tracker, and once the new boiler's in, add its service date to your home maintenance calendar so the next check-up doesn't slip.

If your boiler is over a decade old and the next repair quote comes in above roughly a third of a full replacement, the maths points toward replacing now rather than paying for another repair on borrowed time.