What Happens During an Annual Boiler Service?

Visual inspection

The engineer starts by checking the boiler and its surroundings. They look for any signs of leaks, corrosion, or damage to the casing, pipework, and flue. They also check that the boiler is properly ventilated and that nothing is stored too close to it.

Internal inspection and cleaning

The engineer removes the boiler casing and inspects the internal components - the burner, heat exchanger, ignition leads, and electrodes. They clean any components that have built up with dust or debris and check for signs of wear.

Gas pressure and flow checks

Using a manometer, the engineer tests the gas pressure at the meter and at the boiler. They check that the gas rate matches the manufacturer’s specification. Incorrect gas pressure can cause the boiler to run inefficiently or unsafely.

Flue gas analysis

The engineer uses a flue gas analyser to measure the combustion gases coming out of the flue. This confirms the boiler is burning gas cleanly and not producing dangerous levels of carbon monoxide. The readings must fall within safe limits.

Safety device checks

All safety devices are tested - the pressure relief valve, the overheat thermostat, and the gas valve. The engineer also checks the condensate trap and drain to make sure they are clear.

Final checks and paperwork

The engineer checks the system pressure, tests the controls and thermostat, and makes sure the boiler fires up and shuts down correctly. They will talk you through anything they found and give you a service record. If any repairs are needed, they will quote you before doing any extra work. See also: boiler service vs boiler repair.