What happens during a boiler annual service?
Not sure if this matches your problem?
Use our interactive tool — answer a few questions and get a personalised diagnosis.
Most likely cause & what to check
The engineer should start by checking all gas pipework for leaks using a detector. They'll inspect the flue terminal outside for any blockages or damage.
They remove the boiler casing and visually inspect the heat exchanger, burner, and ignition electrodes for corrosion, cracking, or scaling.
The burner is checked for correct flame shape and colour — a blue flame is healthy. A lazy orange or yellow flame indicates incomplete combustion and carbon monoxide risk.
They check the gas pressure and flow rate against the manufacturer's specifications. Incorrect pressure causes poor combustion and inefficiency.
The flue gases are tested with a combustion analyser inserted into the flue. This checks carbon monoxide levels and combustion efficiency.
All seals, gaskets, and condensate traps are inspected and cleaned. The condensate pipe is checked for blockages or incorrect fall.
Controls are tested: thermostat, programmer, motorised valves, and safety lockout. The engineer should confirm everything cycles correctly before leaving.
You should receive a service record — often a sticker on the boiler plus a written or emailed report. Keep this for warranty and insurance purposes.
Prefer to have it done for you?
Find me an engineer →Was this guide helpful?