Before the appointment
If you know the boiler make, model or last service date, have that information ready. Note any changes in performance, unusual noises, fault codes, pressure changes or problems with heating or hot water. A routine service is easier to plan when the engineer knows whether the appliance is simply due for a check or is already showing a fault.
What a service may check
The checks depend on the boiler and installation. They can include a visual inspection, combustion and flue checks, gas pressure or performance checks where applicable, and inspection or cleaning of accessible components where required. The purpose is to review safety, operation and condition; it is not a guarantee that a fault will never occur.
After the service
Keep the service record and check the manufacturer’s warranty requirements. If the engineer identifies a repair or recommends cleaning, ask what was found and what could happen if it is left. For a boiler that is already unreliable, read the boiler repair guide rather than treating a routine service as a substitute for diagnosis.