Most people book a boiler service, an engineer turns up, twenty minutes later they leave, and nothing is written down. If you have wondered what does a boiler service include beyond that, a real one takes considerably longer, involves taking the casing off, and ends with a document. A quick look at the flame is not a service - and it is not what your warranty requires you to have had.
The short answer
A proper annual service means an engineer who is Gas Safe registered for your appliance type removes the boiler casing, inspects and cleans the key components, checks gas pressure and rate against the manufacturer’s data plate, runs a combustion analysis where the appliance requires it, checks the flue and its terminal, tests the safety devices, confirms adequate ventilation, and gives you a written service record. Expect it to take roughly an hour on a typical combi, longer on a system boiler with a cylinder.
Why it matters more than it sounds
Three reasons, only one of which is about breakdowns.
Safety. A poorly burning appliance or a compromised flue produces carbon monoxide, which you cannot smell, see or taste. The annual check is the only routine thing standing between a degrading heat exchanger and a problem you will not notice until it is serious.
Your warranty. Nearly every manufacturer’s warranty is conditional on an annual service by a qualified engineer, recorded in the benchmark checklist or equivalent. No record, no claim - and manufacturers do ask. A seven-year warranty with no service history is often worth nothing.
Your insurance. Some policies expect you to maintain appliances properly. It is rarely the first question asked, but it can become one after a water damage claim traced to the heating system.
The checklist - what should actually happen
Not every item applies to every appliance, and the manufacturer’s instructions take precedence, but this is the shape of it.
Before touching anything
Check appliance type, model and serial number against the data plate.
Ask about symptoms - noises, pressure loss, radiators not heating, hot water going cold.
Check the appliance location and that any compartment is compliant.
Visual and physical inspection
Remove the casing. This is the step that gets skipped.
Inspect the heat exchanger, burner, injectors and electrodes for corrosion, sooting or debris, cleaning as specified.
Check the condensate trap and pipework, including whether any external run is insulated and correctly sized - the commonest winter lockout.
Inspect the expansion vessel charge and pressure relief discharge.
Check seals and joints for gas soundness.
Performance checks
Test the gas working pressure and the gas rate against the data plate.
Carry out a combustion analysis with a calibrated flue gas analyser where the appliance requires it, and record the readings.
Check the flue and terminal internally and externally for condition, correct termination and clearances.
Confirm ventilation is adequate for the appliance and the room.
Safety devices and controls
Test the flame supervision device and any overheat or thermostat cut-outs.
Check system pressure, filling loop arrangement and the pressure relief valve.
Check the electrical connections, fusing and earth continuity at the appliance.
Confirm controls and thermostat operate as intended.
At the end
A written service record or completed benchmark entry, with readings.
A clear statement of anything that failed, is near end of life, or needs attention.
If the appliance is unsafe, a warning notice and, in some cases, disconnection.
How to check the engineer
Anyone working on a gas appliance in the UK must be on the Gas Safe Register. It is not a trade association you can join - it is the legal requirement.
Ask for the ID card and look at it. The front carries a photo, licence number and expiry date. The back is the part that matters, and almost nobody turns it over: it lists the categories of work the engineer is qualified for. An engineer qualified on cookers is not thereby qualified on your boiler. Check the number on the Gas Safe Register website while they fetch their bag.
If a service is over in twenty minutes and the casing never came off, you did not have a service - you had a visit, and you should say so. This is the part homeowners find awkward and should not. You are entitled to ask what was checked, to see the flue gas analyser readings, and to receive a written record. A good engineer expects those questions and will show you the analyser screen without being asked. Anyone who bristles at them has told you what you need to know.
Landlord or homeowner - what is legally required
If you rent out a property, an annual gas safety check by a Gas Safe registered engineer is a legal duty, producing a gas safety record - the document most people still call a CP12 - which must be given to the tenant.
If you live in your own home, there is no equivalent statutory requirement to have the boiler serviced. Your obligations come from the warranty, the insurance policy and common sense. That catches people out both ways: owner-occupiers who assume it is compulsory, and landlords who assume a service is the same as a gas safety check. It is not - they overlap but are different work, so say which one you are booking.
What to do in the next 30 minutes
Find your boiler’s make, model and serial number from the data plate and write them down.
Find the installation date and check whether the manufacturer’s warranty is still running, and what it requires.
Look for last year’s service record. If you cannot find it, that is your answer on whether the service history is intact.
Book the service now rather than in November - engineers are least busy before the heating season, and a fault found in September is fixed at leisure.
Check whether your boiler cover plan already includes an annual service you are not using.
The service record is worthless if you cannot produce it two years later for a warranty claim or a house sale. Home+ gives you a free place to keep every service record against the boiler itself, with the next service date set as a reminder and the warranty terms attached. Track your boiler service in Home+ as soon as the engineer hands you the sheet.
FAQ
How long should a boiler service take? Roughly an hour for a typical combi, longer for a system boiler with a cylinder or an older appliance. Twenty minutes without the casing coming off is not a service.
Is an annual boiler service a legal requirement? Not for owner-occupiers. Landlords must arrange an annual gas safety check by a Gas Safe registered engineer and provide the record to tenants. For homeowners, the requirement usually comes from the warranty rather than the law.
What is the difference between a gas safety check and a service? A safety check confirms the appliance is safe to use. A service includes that plus cleaning, performance testing and preventative maintenance to manufacturer specification. Landlords need the former; warranties normally require the latter.
How do I check an engineer is Gas Safe registered? Ask for the ID card, check the photo and expiry date, turn it over to see which appliance categories they are qualified for, and verify the licence number on the Gas Safe Register website.
What paperwork should I get afterwards? A written service record or completed benchmark entry listing what was checked and the readings taken, plus a clear note of any defect or component nearing end of life. Keep it - warranty claims depend on it.
Should I service an old boiler that is due to be replaced? Yes, while it is still in use. Safety does not wait for a replacement decision, and a service will often tell you how much life is genuinely left rather than leaving you guessing.
