How often should a boiler be serviced?

Once a year, and ideally in the autumn before the heating season starts rather than during the first cold snap when every other boiler in London is also being checked. That is the short answer. The reasons behind it are worth knowing, because they explain why skipping a year costs more than it looks like it saves.

The warranty reason

Almost every boiler manufacturer’s warranty is conditional on an annual service by a Gas Safe registered engineer, recorded and available if a claim is ever made. A boiler that fails in year six with a five-year-old missed service has a warranty claim that can be refused on exactly that gap — not because the missed service caused the fault, but because the condition of cover was not met.

The legal reason, if you are a landlord

A landlord gas safety certificate has to be renewed every twelve months regardless of whether a boiler service happens on the same visit — they are technically two different things, though most engineers do them together in one visit for efficiency. See our page on gas safety certificates for what that check actually covers and how the renewal timing works.

What an annual service actually checks

A case-off inspection of the internal components, a check of the flue for correct operation, the gas pressure and burner combustion, safety devices, and a visual check of pipework and condensate. It is a safety and efficiency check — it does not repair anything it finds, and it is not the same visit as a repair. If a service turns up a fault, that gets quoted separately under boiler repair.

What skipping it actually risks

Beyond the warranty point, an unserviced boiler runs less efficiently as burners get slightly dirty and settings drift, and a fault that would have been caught early — a warning sign on a heat exchanger, a marginal flue reading — gets more expensive the longer it runs unnoticed. None of that is dramatic on its own, which is exactly why it is easy to let slide for a year, then two.

If your boiler is old enough that you are weighing up a service against starting to think about replacement, our page on boiler replacement covers how to make that call properly rather than guessing.