Servicing
What's Actually Included In A Boiler Service?
Reviewed by our Gas Safe registered engineers · Last updated 22 July 2026
‘Service’ gets used loosely, and not every visit covers the same ground. Here’s exactly what a proper annual boiler service involves, step by step, so you know what you’re paying for and what to expect the engineer to check.
Quick answer: a proper annual service is a visual inspection, gas pressure check, combustion analysis (the key safety test), a heat-exchanger and internal check, safety-device testing, a system pressure and full-cycle operation check, and a written service record. It takes 30–45 minutes and runs roughly £70–£120.
Step By Step
What a proper service covers, step by step
- Visual inspection and case removal. The engineer opens the casing and checks for corrosion, leaks, staining or damage, giving a baseline read on the boiler's condition.
- Gas pressure and flow rate check. Gas pressure is measured at the meter and the boiler's inlet to confirm the correct supply — too low or high and the boiler underperforms or runs unsafely.
- Combustion analysis. A flue gas analyser measures the ratio of gases in the exhaust. This is the single most important safety check — it's how the engineer confirms the boiler burns gas cleanly and isn't producing dangerous carbon monoxide.
- Heat exchanger and internal component check. Depending on the boiler and manufacturer guidance, the heat exchanger, burner and internal seals are inspected for wear, scale or early signs of failure.
- Safety device testing. Safety cut-offs, including the flame failure device and overheat thermostat, are tested to confirm they'll trigger correctly if something goes wrong before next year's service.
- System pressure and general operation check. System pressure is confirmed, the boiler is run through a full fire-up and shut-down cycle, and anything beyond a routine service is flagged.
- Paperwork and certification. You're left with a written service record of what was checked and any findings. For landlords this is separate from your annual Gas Safety Certificate (CP12).
Costs & Duration
What it costs and how long it takes
If the engineer finds a fault during the service, they’ll quote for the repair separately rather than folding it into the service price. You’ll always get an upfront quote before any work starts.
FAQs
Boiler servicing — your questions answered
Does a service include parts, or just checks?
A standard service is checks and adjustments only, not parts replacement. If a component needs replacing, that’s quoted and carried out separately once you’ve approved it.
Do I need to be home for the whole visit?
Yes — someone needs to be present to provide access throughout, since the engineer needs to reach the boiler, the gas meter, and sometimes radiators during the checks.
What happens if the engineer finds something unsafe during the service?
If something poses an immediate safety risk, such as a serious combustion fault, the engineer will explain the issue, may need to isolate the appliance until it’s fixed, and will quote you for the necessary repair.
Is a boiler service the same thing as a power flush?
No — a power flush is a separate, more involved process that clears sludge and debris from the whole heating system, and isn’t part of a standard annual service.
Does servicing a boiler affect the manufacturer's warranty?
Most manufacturers require an annual service by a qualified engineer to keep the warranty valid, so skipping a year can actually invalidate cover if something goes wrong later.
Can I watch the engineer carry out the service?
You’re welcome to be in the room and ask questions as they go — most engineers are happy to explain what they’re checking and why, and it’s a good way to understand your system. Just give them space to work safely, particularly during combustion analysis and casing removal.
Does a combi service differ from a system or regular boiler service?
The core checks (combustion analysis, gas pressure, safety devices) are broadly the same across all three, though a system or regular boiler service may also include a look at the cylinder and, for regular boilers, the header tank, since these extra components are part of the overall system.
Related
Related servicing guides
Why it matters and how often.
Read guideMaintenanceSigns Your Boiler Needs ServicingHow to tell yours is overdue.
Read guideMaintenanceBoiler Maintenance ChecklistSimple checks between visits.
Read guideMaintenanceMaintenanceThe full year-round overview.
Read guidesLandlords: a service is separate from your annual Gas Safety Certificate — see Landlord Certificates. We carry out annual servicing across Southwark, Lambeth and Merton, plus the rest of our coverage area.
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Our Gas Safe registered engineers cover every check on this list, with a written record every time. Gas Safe registered, North London, upfront pricing.
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