Trades guideHeating service
Boiler repair: a Gas Safe engineer and when to repair vs replace
Boiler repair must be done by a Gas Safe registered engineer. Common faults include low pressure, a failed diverter valve, a faulty pump and ignition problems. A common rule of thumb, the rule-of-half, helps decide repair versus replace: once a repair tops half the cost of a new boiler on a unit over ten years old, replacing usually wins. We read your enquiry and reply by email; we do not pass your enquiry to a trade.
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Common boiler faults
- Low pressure, often a leak, a failed expansion vessel or a faulty valve.
- No hot water but heating works, usually a diverter valve.
- No heating and no hot water, often a pump or PCB fault.
- Kettling or banging noises, a sign of sludge or scale.
- Repeated lockouts or ignition faults.
Repair or replace
Apply the rule-of-half, a common rule of thumb rather than a formal standard: if the repair quote is more than half the cost of a new boiler and the unit is over ten years old, replacing is usually the better value over the next few years. Below that threshold, repair.
What it costs
- Boiler repair
- Get a quote Depends on the fault and parts. A fair engineer diagnoses and quotes before fitting parts.
- Repair vs replace
- The rule-of-half Repair above half the cost of a new boiler on an over-ten-year-old unit rarely pays.
How to choose a trade
- Use a Gas Safe registered engineer and verify the registration number; gas work is illegal otherwise.
- Ask the engineer to show the fault diagnosis and quote before fitting parts.
- If the repair tops half the cost of a new boiler on an old unit, ask for a replacement quote too.
Frequently asked questions
Who can legally repair a gas boiler?
Only a Gas Safe registered engineer. It is illegal for anyone not on the register to work on a gas boiler, and unregistered work can void your warranty and your insurance. Always verify the engineer Gas Safe registration number before they start.
Is it worth repairing an old boiler?
Often, yes, if the fault is a single part and the boiler is otherwise reliable. For an older boiler with a large repair quote, use the repair-or-replace rule of thumb above and ask the engineer for a like-for-like replacement quote so you can compare the two in writing.
My boiler has no hot water but heating works, is it serious?
Usually not an emergency. That pattern points to a diverter valve rather than a major failure, so a planned daytime appointment is far cheaper than an out-of-hours callout. A Gas Safe engineer can confirm the fault and quote the repair.
Sources
Editor, VettedHome
Adam leads VettedHome's editorial coverage of UK home services. He is the founder and managing director of Muswell Rose, the commercial strategy and modern systems business behind a portfolio of UK information sites, and he researches and writes the plain-English guides that help homeowners choose between installers and trades, drawing on the standards set by the relevant bodies for each job, such as Gas Safe Register, NICEIC, MCS, TrustMark and the Property Care Association. He is clear about what to check before any work starts.
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