The engineer has been out twice this winter. Both times the fix worked, both times the invoice stung, and now there is a new noise. At some point the question stops being 'what is wrong with it' and becomes 'how much longer am I going to keep paying to find out'. Nobody can answer that with certainty, but there is a way of thinking about it that keeps the decision yours rather than the engineer's.
Start with the age and the parts
A gas boiler that has been serviced annually and is under ten years old is usually worth repairing, because the fault is likely to be one component and the rest of the appliance has life left in it. Past fifteen years the calculation shifts. Parts for older models become harder to source, the efficiency is lower than anything sold now, and a run of repairs starts to add up to a meaningful share of a replacement. Ask the engineer two direct questions: is the part still readily available, and what else on this boiler is of a similar age and likely to go next. Heat exchangers and circuit boards are the expensive ones; if either is the fault on an old boiler, a straight comparison with a new unit is warranted.
Repairs that are worth doing
Some faults are cheap and fully resolve the problem. A diverter valve, a pump, a fan, a pressure sensor, a blocked condensate pipe: these are routine and an engineer who does breakdown work carries or can get them quickly. A boiler that keeps losing pressure may have nothing wrong with it at all; the leak is usually somewhere in the pipework or a radiator valve, and replacing the boiler will not stop it. Be wary of anyone who moves to 'you need a new boiler' before they have diagnosed the fault. Good engineers tell you what is wrong first and let you decide.
When replacing is the better money
Replacement makes sense when the repair bill is a large fraction of a new boiler, when the model is obsolete and parts are on back order, when the heat exchanger has failed, or when the boiler is so inefficient that the running costs are doing the damage rather than the repair bills. It also makes sense when the system is changing anyway: a loft conversion adding radiators, a move to an unvented cylinder, or a plan to add a smart control that the existing boiler cannot talk to.
A replacement is more than a box swap. The engineer should flush or at least clean the system, fit a magnetic filter if there is not one, check the gas supply pipe is sized for the new appliance, and register the installation so the manufacturer's guarantee is valid. Guarantees on new boilers vary by brand and installer, and they nearly always depend on an annual service being done and recorded. Ask what guarantee you would get and what it requires of you.
Whoever does it must be registered
Repair or replace, this is gas work, and the law requires a Gas Safe registered engineer. Ask for the registration number, check it on the public register, and look at the card when they arrive. On a replacement, the installer must also notify the work so you receive a building regulations compliance certificate; you will want that when you sell the house.
The listings on this site include 3,554 plumbers, and many of them describe boiler repair, servicing or installation among their services. Browse heating engineers near you, or describe the fault, the boiler's age and model, and request quotes for both a repair and a replacement. Getting both prices on paper is the quickest way to make the decision feel less like a gamble.
