A boiler service is a yearly check that keeps the appliance running safely and efficiently. It is not the same as a repair. The engineer inspects, tests and cleans the parts that matter, then records what was found. Knowing what happens on the visit makes it easier to prepare and to ask the right questions.
Before the visit
Clear access to the boiler, and to the flue outside if you can reach it safely from ground level. Move stored items, make sure the boiler and its controls are reachable, and note any unusual noises, smells or pressure changes. Have last year's service record to hand. If you rent, let the landlord or agent know, and make sure someone will be at home to let the engineer in.
What the engineer checks
The exact list depends on the boiler, but a thorough service usually covers the following.
- The condition of the boiler case, the pipework and the seals around the case.
- The flue and the ventilation, including the outside terminal where it can be reached.
- Gas pressure and the combustion readings, taken with a calibrated analyser.
- The safety devices, including the flame failure and overheat controls.
- The condensate trap and pipe, cleared and checked for blockages.
- The water pressure, the expansion vessel and the pressure relief valve.
- The controls, thermostat and programmer, checked against the heating and hot water.
- The inside of the appliance, cleaned where the manufacturer allows it.
The engineer works on the appliance with the case on or removed as the manufacturer's instructions allow. You do not need to open anything yourself, and you should not.
Gas safety and the flue
A gas boiler needs a clear flue and enough ventilation to burn safely. The engineer checks that the products of combustion leave the building and that no exhaust gas can come back into the room. If the flue is damaged or the ventilation is blocked, the engineer will explain what needs to change before the boiler can be used safely. This is one reason a service is more than an annual formality.
What is not included
A service does not normally include parts, a repair, a power flush or descaling. If the engineer finds a worn part, they should explain it and quote before doing any extra work. A boiler that has not been serviced for several years may need more than one visit, and the record will say so.
The service record
You should receive a written record of the visit, including the readings taken and any faults found. Keep it with the boiler instructions. It shows the appliance has been maintained and helps the next engineer see what has changed. If you move home, leave the record with the appliance so the next owner or tenant has the history. If you are a landlord, the record belongs with your safety paperwork, though a service and a gas safety check are separate tasks. Ask the engineer to explain any reading you do not understand, and note the advice they give about the next visit.
