What Is Included in a Boiler Service? Full 11-Step Checklist
A proper boiler service involves 11 distinct checks taking 30-60 minutes. Here is exactly what a Gas Safe engineer should do, and what it means for your boiler safety and efficiency.
The 11 Steps of a Boiler Service
The engineer inspects the boiler casing, flue outlet, and visible pipework for damage, corrosion, or signs of leaks. They check the flue terminal is not blocked and has adequate clearance.
Using a calibrated gauge, the engineer checks the gas supply pressure and flow rate. Correct pressure ensures efficient combustion. Low pressure can indicate a supply issue; high pressure can damage the burner.
Using an electronic flue gas analyser, the engineer measures CO, CO2, and combustion efficiency. This is mandatory for a proper service. An engineer who skips this is not completing a full service.
The burner is removed, inspected for damage and carbon deposits, and cleaned. A dirty burner produces incomplete combustion, increased CO output, and reduced efficiency.
The engineer checks for blockages (limescale, debris) and corrosion. A blocked heat exchanger causes overheating and eventual failure costing £400-800. Regular cleaning significantly extends its life.
All seals and gaskets around the combustion chamber and flue connections are inspected for deterioration or leaks. A failing seal can allow combustion gases including CO to escape into the property.
The engineer checks the condensate trap is clear and the drain is unobstructed. A blocked condensate trap is one of the most common causes of boiler shutdown in winter, often triggered by freezing.
All safety devices are tested: overheat thermostat, pressure relief valve, flue blockage detection, and gas valve. These devices prevent dangerous failures and must be verified at every service.
The engineer checks system pressure (should be 1-1.5 bar when cold) and inspects the expansion vessel. A failed expansion vessel causes erratic pressure and pressure relief valve discharge.
The engineer tests the boiler responds correctly to the thermostat and programmer, checking the boiler ignites cleanly when called for heat.
All readings are recorded: gas pressure, flue gas analysis results, CO/CO2 levels, combustion efficiency, and system pressure. The signed service report must include the engineer Gas Safe registration number.
How Long Does a Boiler Service Take?
| Boiler Type | Typical Duration | Notes |
|---|---|---|
| Combi boiler | 30-45 minutes | Simplest - no cylinder or tanks |
| System boiler | 40-55 minutes | Cylinder check adds 10-15 minutes |
| Conventional boiler | 50-75 minutes | Most complex - multiple tanks to inspect |
| Oil boiler | 45-75 minutes | Nozzle replacement and combustion checks add time |
| Electric boiler | 30-45 minutes | No combustion analysis required |
What Paperwork Should You Get?
- Engineer full name and Gas Safe registration number
- Date of service
- Your boiler make, model, and serial number
- All key readings: gas pressure, flue gas analysis results, CO and CO2 levels, combustion efficiency %
- System pressure reading
- Any issues identified during the service
- Recommendations for further work
- Engineer signature
What a Service Does NOT Include
Red Flags During a Service
- Engineer does not use a flue gas analyser - this is a mandatory check
- Does not show Gas Safe ID card on arrival - you are entitled to see this
- Rushes through in under 20 minutes - a proper service takes at least 30-45 minutes
- Does not provide written paperwork - a service certificate proves the job was done correctly
- Pressures you to book expensive extras immediately - good engineers explain, not pressure
What You CAN Do Yourself
- Check boiler pressure gauge monthly (should read 1-1.5 bar cold)
- Top up pressure if it drops below 1 bar (using the filling loop)
- Bleed radiators if they have cold patches at the top
- Check for visible water leaks around pipework
- Test your carbon monoxide alarm monthly
- In winter, check the condensate pipe has not frozen if your boiler stops
Frequently Asked Questions
How long does a boiler service take?
A standard boiler service takes 30-60 minutes for most gas boilers. Combi boilers take 30-45 minutes; system boilers 40-55 minutes; conventional boilers 50-75 minutes. Oil boiler services take 45-75 minutes due to additional checks including nozzle replacement. An engineer who finishes in under 20 minutes has almost certainly skipped mandatory checks.
What paperwork should I get after a boiler service?
After a boiler service, you should receive a written service report including the engineer full name and Gas Safe registration number, date of service, boiler details, all key readings (flue gas analysis, gas pressure, system pressure), issues found, and recommendations. Keep this document safely for warranty claims, insurance, and when selling your home.
Can I service my own boiler?
No. Under the Gas Safety (Installation and Use) Regulations 1994, only Gas Safe registered engineers can legally work on gas boilers. DIY servicing is illegal, invalidates your warranty, and is extremely dangerous. What you CAN do yourself: check the pressure gauge, bleed radiators, check for visible water leaks, and test your carbon monoxide alarm monthly.