The short answer
Repair the boiler when it is a one-off fault on a unit that is otherwise reliable and parts are available. Consider replacing it when faults keep coming back, parts are obsolete, the heat exchanger or flue is failing, or the boiler no longer suits how you use hot water. An engineer's diagnosis should come first, so you are deciding on facts rather than guesses.
Start with a proper diagnosis
A boiler that has stopped working is not automatically a boiler that needs replacing. Many breakdowns come down to a single component such as a pump, diverter valve, fan, sensor or ignition part. The first job is to find out exactly what has failed and why, then decide. Beware of anyone who recommends a new boiler without testing the old one.
When repairing makes sense
In these cases a repair usually gives the best value, and the boiler can carry on for years.
- It is the first significant fault in several years
- The boiler has been serviced regularly
- The failed part is available and the fault is clearly identified
- The heat exchanger, flue and casing are in good condition
- The boiler still suits the household's hot water use
When replacement is worth considering
When several of these apply, money spent on repairs tends to buy time rather than reliability.
- The same fault keeps returning after repairs
- Parts are discontinued or hard to source
- The heat exchanger is leaking or badly corroded
- The flue or case no longer meets current standards
- The household has changed, for example an extra bathroom
- The system is a non-condensing or back boiler set-up
Efficiency and running costs
Modern condensing boilers reuse heat that older non-condensing boilers send out of the flue. If your boiler predates condensing technology, a replacement usually burns less fuel for the same warmth. How much you save depends on your house, your usage and your fuel, so treat any fixed savings figure with caution.
Gas and oil are different
Oil boilers often last well when serviced, and many oil faults are down to the burner, filters or supply rather than the boiler itself. On an oil system, check the tank and supply line before deciding the boiler is at fault. On gas, repeated pressure loss or leaks inside the case often point to a worn heat exchanger, which is one of the most common reasons to replace.
If you decide to replace
Use the replacement as a chance to review boiler type, controls and system health. A system flush and inhibitor protect the new boiler, and good controls make a larger difference to comfort than most people expect. A like-for-like swap can usually be finished in a single day; conversions take longer.
Questions to ask the engineer
Once the fault is found, a few direct questions make the decision easier. Ask what failed and why, whether the cause is wear or something in the wider system such as sludge or low pressure, and whether other parts are showing similar wear. Ask whether parts for your model are still readily available. Ask what the boiler's flue, seals and heat exchanger look like. A clear answer to each lets you weigh one repair against the likelihood of the next, rather than deciding under pressure on a cold morning.
Frequently asked questions
My boiler has broken down. Should I replace it straight away?
No. Get it diagnosed first. Many breakdowns are a single part that can be replaced, and the diagnosis tells you whether the rest of the boiler is sound.
Is an old boiler always less efficient?
Older non-condensing boilers are generally less efficient than modern condensing ones. A condensing boiler that is ten years old but well serviced can still be perfectly sound.
Do you repair oil boilers as well as gas?
Yes. Maintenance, repairs and oil boiler repairs are all listed services, and the business is registered for both fuels.
How long does a boiler replacement take?
A like-for-like swap can usually be completed in a single day. Changing boiler type or moving the boiler adds time, which the survey will confirm.
Related pages
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