A boiler service typically includes a visual inspection, checks of the boiler and heating controls, inspection of internal components, flue and combustion checks, and cleaning where necessary. The engineer will also look for problems such as leaks or corrosion and confirm that the boiler is operating safely.
For a gas boiler, the service should be carried out by a suitably qualified Gas Safe registered engineer. A typical appointment takes around 40 minutes to an hour, although this varies according to the boiler’s age, type and condition.
Exactly what happens can also vary by boiler and manufacturer. The engineer should follow the servicing requirements for the appliance rather than working from one universal checklist.
Boiler service checklist
Although the exact procedure depends on the boiler and its manufacturer’s servicing instructions, there are several checks you can typically expect during a gas boiler service.
During the service
☐ Visual inspection of the boiler and accessible pipework
☐ Check for visible leaks, corrosion or damage
☐ Check the boiler and heating controls
☐ Inspect relevant internal boiler components
☐ Check the flue and its condition
☐ Carry out combustion checks where required
☐ Check boiler pressure and operation
☐ Check relevant safety devices
☐ Clean components where required
☐ Check heating and hot-water operation
☐ Identify faults or repairs that may be needed
Before the engineer leaves
☐ Ask whether any problems were found
☐ Find out whether recommended repairs will cost extra
☐ Receive a service certificate or completed service record
☐ Keep the paperwork for your records and boiler guarantee
This isn’t a universal checklist that every engineer must follow in exactly the same order. The boiler’s make, model, age and condition determine the precise servicing procedure, and the engineer should follow the manufacturer’s instructions.
Worcester Bosch, for example, says its servicing typically includes visual inspection of the flue, checking CO2 readings at the gas valve, testing fan pressure across the heat cell, cleaning the heat exchanger where required and recording heating and water readings.
1. Visual inspection
The engineer normally begins by looking at the boiler, its installation and accessible surrounding components.
They will check for signs such as:
- Water leaks
- Corrosion
- Damage to the boiler or pipework
- Problems around the flue
- Anything else suggesting that the installation isn’t operating as expected
This initial inspection can also help the engineer decide whether any particular part of the boiler needs closer attention.
2. Boiler and heating controls
The engineer should check that the boiler’s controls operate correctly.
Depending on the system, this could involve checking how the boiler responds to a demand for heating or hot water and confirming that it starts and stops correctly.
Tell the engineer about any problems you’ve noticed with your thermostat, programmer or boiler controls before the service starts. A fault that only occurs occasionally may not appear during the appointment.
3. Internal boiler components
Servicing isn’t normally limited to looking at the outside of the boiler.
An engineer may remove the boiler’s front cover to inspect internal parts for faults, damage or areas requiring cleaning.
What needs inspecting or cleaning depends on the boiler’s design and condition. Components such as the burner and heat exchanger may require attention according to the manufacturer’s servicing instructions.
This is one reason boiler servicing isn’t a DIY maintenance job. Removing the casing of a gas boiler and carrying out internal servicing should be left to an appropriately qualified professional.
4. Flue and combustion checks
The flue carries combustion products safely away from the boiler, so checking it is an important part of servicing.
The engineer may use a flue gas analyser to check combustion performance. This helps establish whether the boiler is burning gas correctly and operating within the appropriate parameters for that appliance.
The exact testing procedure should follow the manufacturer’s instructions.
5. Boiler pressure and performance
The engineer will also check how the boiler performs while operating.
This can include checking relevant pressures and confirming that the boiler provides heating and hot water correctly.
If you’ve noticed the boiler pressure repeatedly falling or rising, tell the engineer before the service. Persistent pressure problems may indicate a fault requiring further investigation rather than routine servicing alone.
6. Cleaning where necessary
A boiler service doesn’t necessarily mean every internal component is dismantled and cleaned every year.
Cleaning should be carried out where required by the boiler’s condition and manufacturer’s servicing instructions.
Worcester Bosch, for example, specifies that its heat exchanger is cleaned if required, rather than describing this as an automatic part of every service.
Filter systems fitted to the central heating system may be cleaned during servicing.
This distinction matters because different boilers have different servicing requirements. A checklist claiming that every engineer must clean exactly the same components during every appointment can be misleading.
7. Safety and operational checks
Before finishing, the engineer should establish that the boiler operates safely and correctly.
If the engineer finds a safety problem, they should explain what is wrong and what needs to happen next.
A service can identify faults, but that doesn’t necessarily mean repairing those faults is included in the price.
8. Service record and paperwork
At the end of the appointment, you should receive a record that the boiler has been serviced.
Keep this paperwork, particularly while the boiler is under a manufacturer guarantee.
Worcester Bosch, for example, requires its boilers to be serviced annually to maintain its manufacturer guarantee. Other manufacturers can have their own conditions, so check the terms covering your boiler.
What isn’t normally included in a boiler service?
A boiler service is preventative maintenance and inspection. It shouldn’t be confused with a boiler repair.
A standard service will not necessarily include:
- Replacement parts
- Repairing an existing fault
- Extensive fault-finding
- A powerflush
- Major central-heating repairs
- Replacing radiators or valves
- Fixing concealed pipe leaks
If the engineer discovers a fault, they may be able to repair it during the same visit, but don’t assume the service price includes the additional labour and parts.
Ask before the appointment what happens if a repair is required and whether you will receive a separate quotation.
How long does a boiler service take?
A typical boiler service takes around 40 minutes to one hour. It can take longer if the boiler is difficult to access, requires cleaning, or the engineer discovers something that needs further investigation.
Speed alone doesn’t tell you whether a service was carried out correctly. Different boilers have different servicing procedures, so the important question is whether the engineer completed the checks required for your appliance.
How often should a boiler be serviced?
For most households, once a year is the standard recommendation.
Annual servicing may also be a condition of the manufacturer’s guarantee. Worcester Bosch explicitly requires yearly servicing to maintain its guarantee.
Check your own boiler’s warranty or guarantee terms rather than assuming every manufacturer has identical requirements.
Who can service a gas boiler?
Gas-boiler servicing should be carried out by an appropriately qualified Gas Safe registered engineer.
You can check an engineer’s registration and the categories of gas work they’re qualified to undertake through the Gas Safe Register.
Oil boilers have different requirements. Gas boilers should be serviced by a Gas Safe registered engineer, while oil boilers should be serviced by a suitably qualified technician, such as one registered with OFTEC.
Is a boiler service the same as a gas safety check?
No. Although there can be overlap, a boiler service and a landlord gas safety check are not the same thing.
A boiler service focuses on the condition, performance and maintenance of the boiler. A landlord’s gas safety check is a statutory safety inspection covering relevant gas appliances and flues in rented accommodation.
Landlords have specific legal duties concerning gas safety. HSE guidance states that landlords must arrange annual gas safety checks on gas appliances and flues they provide and maintain gas appliances, flues and associated pipework in a safe condition (HSE).
A landlord should therefore not assume that booking an ordinary boiler service automatically fulfils all of their gas-safety obligations.
How should you prepare for a boiler service?
There isn’t much you need to do beforehand, but making the boiler easily accessible can save time.
Clear belongings away from the boiler and make sure the engineer can reach it safely. If you still have the boiler manual or previous service records, have them available.
It is also useful to make a note of anything unusual you’ve noticed, such as:
- Pressure regularly dropping
- Unusual noises
- Intermittent fault codes
- Heating taking longer than usual
- Problems with hot water
- Radiators heating unevenly
Tell the engineer about these symptoms before they begin. A routine service may not include extensive fault-finding, but the information can help identify something that deserves closer investigation.
Frequently asked questions
Does a boiler service include cleaning?
Cleaning can be included where necessary, but not every component is automatically cleaned during every service.
Does a boiler service include checking radiators?
A boiler service primarily concerns the boiler and relevant heating-system checks. The exact scope varies between providers, so homeowners shouldn’t assume every standard service includes a full radiator inspection.
Will an engineer fix problems during a boiler service?
Not necessarily. The engineer may identify faults during the service, but repairs and replacement parts can be charged separately. Ask what is included in the quoted service price before the appointment.
Do you get a certificate after a boiler service?
You should receive a certificate showing that the boiler has been serviced, or the engineer may complete the service record in the boiler manual.
Does a boiler need servicing every year?
Annual servicing is generally recommended for gas boilers. It may also be required to maintain a manufacturer’s guarantee; Worcester Bosch, for example, makes yearly servicing a condition of its guarantee.
Can I service my own boiler?
No. While homeowners can carry out simple external checks, internal gas-boiler servicing should be carried out by an appropriately qualified Gas Safe registered engineer.
Sources
Worcester Bosch, How often should a boiler be serviced? (https://www.worcester-bosch.co.uk/how-often-should-a-boiler-be-serviced)
Worcester Bosch, In Guarantee Service (https://www.worcester-bosch.co.uk/support/boiler-service/guarantee-service)
Health and Safety Executive, Gas safety – landlords and letting agents (https://www.hse.gov.uk/gas/landlords/)
Gas Safe Register, Check the Register (https://www.gassaferegister.co.uk/find-an-engineer-or-check-the-register/)
Accurate as of: 20 August 2026