Heating 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. The rule-of-half decides repair versus replace: once a repair tops half the cost of a new boiler on a unit over ten years old, replacing usually wins. Sorted Property matches you to a vetted engineer.
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Get matchedCommon 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: if the repair quote is more than half the cost of a new boiler and the unit is over ten years old, replacing usually wins on a five-year total cost. Below that threshold, repair. An old boiler tends to need another major repair within a few years, so paying half-cost now often means paying again before payback.
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 vetted 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?
Apply the rule-of-half. If the repair quote is more than half the cost of a new boiler and the unit is over ten years old, replacing usually wins on a five-year total cost. Below that, repair. Old boilers tend to need another major repair within a few years, which tips the maths.
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, Sorted Property
Oliver leads Sorted Property's editorial coverage of UK home services. He researches and writes the plain-English guides that help homeowners choose between installers and trades, drawing on the standards set by bodies such as MCS, TrustMark, the Energy Saving Trust and the Property Care Association, and is clear about what to check before any work starts.
Last reviewed: 11 June 2026