Boiler Service Checklist: What Your Engineer Should Check
A practical, printable reference for homeowners and landlords. Use this before, during, and after your boiler service to make sure nothing is missed.
Before the Engineer Arrives
- Clear access to the boiler - at least 30cm clearance all sides
- Note down your boiler make, model, and serial number (on a sticker on the boiler)
- Have your last service record or certificate handy
- Check your carbon monoxide alarm is working - press the test button
- Note any issues you have noticed: unusual noises, smells, pressure drops, or leaks
- Check the boiler pressure gauge - note the current reading to tell the engineer
What the Engineer Should Check (11 Steps)
- Visual inspection of boiler casing, flue, and ventilation
- Gas pressure and flow rate test (using calibrated gauge)
- Flue gas analysis with electronic analyser - CO, CO2, and combustion efficiency
- Burner inspection and cleaning (burner removed and cleaned)
- Heat exchanger inspection for blockages and corrosion
- Seal and gasket check around combustion chamber and flue connections
- Condensate trap and drain check (cleared if blocked)
- Safety device tests - overheat thermostat, pressure relief valve, gas valve
- System pressure check and expansion vessel inspection
- Thermostat and controls test - boiler responds correctly to heat demand
- All readings recorded on written service report
After the Service
- Received written service report or certificate
- Report includes engineer full name and Gas Safe registration number
- All readings are recorded (gas pressure, CO/CO2 levels, combustion efficiency %)
- System pressure reading recorded
- Any issues found explained clearly
- Recommendations for future work documented in writing
- Invoice received (not just cash payment)
- Service report filed with your home documents
- Calendar reminder set for next year (aim for May-August)
What Good Readings Look Like
Ask your engineer to explain the flue gas analysis results. Here are the typical good values:
| Reading | Normal Range | Why It Matters |
|---|---|---|
| System pressure (cold) | 1.0-1.5 bar | Too low = airlocks; too high = pressure relief valve risk |
| Gas supply pressure | 18-23 mbar | Low pressure = poor combustion and efficiency |
| CO/CO2 ratio in flue | <0.004 | High ratio = incomplete combustion, CO risk |
| Flue temperature | Varies by boiler | Engineer compares to manufacturer specification |
| Combustion efficiency | 88-92%+ | Lower % = wasted fuel and higher gas bills |
Additional Checklist for Landlords (CP12)
- Confirm engineer is Gas Safe registered before they start
- CP12 covers all gas appliances - boiler, hob, gas fires (not just boiler)
- CP12 certificate received after the check
- Certificate provided to tenant within 28 days
- Digital and paper copies kept for at least 2 years
- Date booked for next year check (same time as this year if possible)
For more detail on landlord requirements, see the full landlord gas safety and CP12 guide.
Frequently Asked Questions
What should I do before the engineer arrives for a boiler service?
Before your boiler service: clear access to the boiler with at least 30cm clearance all sides, note down your boiler make, model, and serial number, have your last service record handy, check your carbon monoxide alarm is working, and note any issues you have noticed recently. The more information you can give the engineer, the more useful the service will be.
What should be on my boiler service checklist?
A complete boiler service checklist includes: visual inspection of boiler and flue, gas pressure test, flue gas analysis with electronic analyser, burner inspection and cleaning, heat exchanger inspection, seal and gasket check, condensate trap check, safety device tests, system pressure check, thermostat and controls test, and a written service report with all readings recorded. The engineer should cover all 11 of these steps.