The short answer
A boiler service is a visual inspection, a strip-down clean of key components and a set of safety tests carried out by a Gas Safe engineer. It typically takes around 45 minutes to an hour. The engineer checks the flue, gas pressure and combustion, cleans parts such as the burner and condensate trap, and confirms the boiler is working safely and efficiently.
The main checks in a service
Exact steps follow the manufacturer's service instructions for your model, but a proper service covers these areas:
- Visual check of the boiler, pipework and flue for signs of damage, corrosion or leaks.
- Flue inspection to make sure exhaust gases are escaping safely and the terminal is clear.
- Gas pressure and flow rate checks at the boiler.
- Combustion analysis using a flue gas analyser, to confirm the boiler is burning correctly.
- Removal and cleaning of components where required, such as the burner, electrodes and condensate trap.
- Checks on seals, the fan and safety devices so the boiler shuts down correctly if something goes wrong.
- System pressure and expansion vessel check.
Why an annual service matters
Most manufacturers require a yearly service by a Gas Safe engineer to keep the boiler warranty valid. Skip a year and a later claim may be refused.
A service also picks up small problems early, before they turn into a breakdown on the coldest night of the year. A boiler that is burning cleanly uses fuel more efficiently, and the combustion checks help protect against carbon monoxide, which cannot be seen or smelled.
Service or gas safety check?
They are not the same thing. A gas safety check confirms that gas appliances are safe to use. A service goes further, cleaning and maintaining the boiler so it keeps running well. Landlords are legally required to have a gas safety check on every gas appliance each year and to give tenants a copy of the record, often called a CP12. Many landlords combine it with a service in the same visit.
What you receive afterwards
At the end of the visit you should get a written record of what was checked, the readings taken and any issues found. If anything needs attention, the engineer will explain it and advise whether it is urgent. Keep this record with your warranty paperwork, as manufacturers may ask for it.
When to book
Late summer and early autumn are ideal, before the heating is needed every day and before engineers get busy with winter breakdowns. If your boiler is still under warranty, book within the window stated in your warranty terms, which is usually every twelve months from installation.
How to prepare for the visit
Clear the space around the boiler and make sure the flue terminal outside can be reached. Have the boiler manual and previous service records to hand if you have them, and note any odd noises, pressure drops or fault codes you have seen during the year so the engineer can look into them.
Signs your boiler needs attention between services
An annual service is the baseline, but some symptoms are worth reporting straight away rather than waiting for the next visit. A yellow or orange flame instead of a crisp blue one can point to poor combustion. Black sooty marks around the casing or flue, a boiler that keeps losing pressure, new banging or whistling noises, and pilot lights on older models that keep going out all suggest something has changed inside.
If a carbon monoxide alarm sounds, or anyone in the home has headaches, dizziness or nausea that ease when they go outside, turn the boiler off, open windows and get it checked before using it again. Every home with a gas boiler should have an audible carbon monoxide alarm fitted in the same room, tested regularly.
Frequently asked questions
How long does a boiler service take?
Usually around 45 minutes to an hour, longer if the boiler needs extra cleaning or a fault is found.
How often should a boiler be serviced?
Once a year. It is the interval most manufacturers require to keep the warranty valid.
Will I lose heating during a service?
The boiler is switched off while it is being worked on, but heating and hot water are back on once the service is finished.
Do you provide landlord gas safety certificates?
Yes, we carry out landlord gas safety checks (CP12) and can combine them with a boiler service in the same visit.