The short answer
Repair a boiler that is under about 10 years old, has been serviced, and has a one-off fault on a common part. Think hard about replacing one that is over 12 years old and has broken down two or three times in two years, or needs a major part such as a circuit board or heat exchanger. Between those two, it comes down to the sums below. Either way, a Gas Safe registered engineer’s diagnosis comes first, because you cannot decide until you know what has failed.
Four questions that decide it
- How old is the boiler? Look for the date on the data badge inside the case flap, or on the installation paperwork. Under 10 years, repair is almost always the answer. Over 12, the next questions carry more weight.
- What has failed? A pump, diverter valve or fan is a routine repair at a typical £150 to £350. A circuit board is £250 to £450. A heat exchanger is the most expensive part in most boilers and, on an older one, often tips the decision.
- How often has it broken down? One repair in five years is normal wear. Three in two years usually means the boiler is wearing out as a whole, and more bills are coming.
- Can the parts still be got? On older or discontinued models, ask the engineer how easy the part is to source. A part that takes two weeks to arrive means two weeks without heating or hot water.
Doing the sums
Put the repair quote next to the cost of a new boiler, then add what you expect to spend on the old one over the next couple of years.
| Compare | Repair | Replace (like-for-like combi) |
|---|---|---|
| Typical upfront cost | £150 to £450, plus £80 to £120 to diagnose | £2,200 to £3,400 fitted |
| Warranty | Usually a guarantee on the part and labour only | A new manufacturer warranty on the whole boiler, if serviced yearly |
| Likely bills over the next few years | Low on a young boiler, rising on an old one | Annual service, typically £80 to £120 |
| Disruption | Often fixed in one visit | Usually a one-day swap |
Prices are typical national figures, checked October 2026.
A simple rule of thumb: if a single repair on a boiler over 12 years old costs more than about a sixth of a new boiler, or you are on your third big repair, put the money towards a replacement instead. Treat it as a starting point. A well-kept 14-year-old boiler with one failed pump is still worth fixing.
When the boiler itself is the problem
Regular lockouts, a corroded heat exchanger, parts that are no longer made or pressure that needs topping up every week (see boiler losing pressure) all push the sums towards replacing. The boiler replacement section lists the full set of warning signs and how to choose a new boiler.
When to stick with a repair
Do not let anyone talk you into a new boiler for a £200 fault on a sound, serviced boiler. A good engineer will tell you when a repair is the sensible spend, and if they push replacement on a young boiler, get a second opinion. Check the warranty first too: if the boiler is still covered and has a service history, the manufacturer may fix it for free. Our boiler repair cost guide covers what each part should cost.
If you are told the boiler is unsafe, it may be classed as “at risk” or “immediately dangerous” and switched off. Ask the engineer to explain the fault in writing. That label is about safety, not a sales pitch, but you are entitled to know exactly what was found.
If you decide to replace
Replacing a boiler is usually a one-day job on a like-for-like swap. Get at least two fixed quotes, and make sure each names the boiler model, its output in kW and the warranty length so you can compare them properly.
Some people use a failed boiler as the moment to look at a heat pump. It can be the right call in a well-insulated home if you plan to stay, but it is a bigger project and rarely a quick fix in the middle of winter. If you need heat this week, a repair or a new combi is the practical answer.
Keep the next boiler going
Whichever way you go, a yearly boiler service is what keeps a warranty valid and catches small faults early. And before any engineer touches the boiler, take two minutes to check they are Gas Safe registered.
City Boiler connects you with independent local engineers who are Gas Safe registered. See the boiler repair page for what a repair visit involves.
Common questions
At what age should a boiler be replaced?
There is no fixed age. Many boilers run well past 15 years with yearly servicing. Age matters when it combines with repeat breakdowns, expensive parts or parts that are no longer made, which becomes more likely after about 12 years.
Is it worth repairing a 15-year-old boiler?
For a cheap, one-off fault such as a pump or valve, often yes. For a circuit board or heat exchanger, or a third breakdown in two years, compare the bill with a new boiler first, because another part is likely to fail soon.
How much does a new boiler cost compared with a repair?
Most repairs cost £150 to £450 plus a diagnostic visit of £80 to £120. A like-for-like combi swap typically costs £2,200 to £3,400 fitted. Both are typical national prices, checked October 2026.
Will a new boiler lower my gas bill?
If your current boiler is an older non-condensing model, a modern condensing boiler should use less gas for the same heat. If you already have a condensing boiler in good order, the saving is smaller, so do not replace a working boiler on running costs alone.