Boiler Service Checklist: What Engineers Check

When a Gas Safe engineer services your boiler, what do they actually do? Many homeowners pay for an annual service without knowing exactly what is included. This guide breaks down the complete boiler service checklist, step by step.

Why a Proper Service Matters

A boiler service is a thorough safety and efficiency inspection that should take between 30 and 60 minutes for a standard combi boiler. If an engineer is in and out in 15 minutes, it is unlikely they have completed a proper service.

The Complete Boiler Service Checklist

1. Visual Inspection

• Check for visible damage, corrosion, or deterioration
• Inspect the flue terminal — must be clear and unobstructed
• Look for signs of previous leaks (staining, rust marks)
• Check pipework connections for corrosion

2. Gas Supply and Pressure

• Check gas inlet pressure at the boiler
• Verify gas rate is within manufacturer specification
• Test for gas leaks at connections using a gas detector
• Test gas valve operation

3. Burner and Combustion

• Remove and inspect the burner for debris or damage
• Clean the burner if necessary
• Carry out flue gas analysis — measuring CO and CO2 in exhaust gases
• Verify combustion is within safe parameters

4. Heat Exchanger

• Inspect for corrosion or cracking
• Check for sooting that reduces efficiency
• Clean if required

5. Flue and Ventilation

• Inspect flue route for damage or blockages
• Check flue joints and seals are intact
• Verify the flue terminal meets current regulations

6. Safety Devices

• Test the overheat thermostat
• Check pressure relief valve is not discharging
• Inspect and test the automatic air vent

7. Water Side Checks

• Check system pressure — typically 1 to 1.5 bar when cold
• Inspect the expansion vessel pressure
• Confirm the pump is circulating water correctly
• Check the condensate trap and pipe on condensing boilers

8. Controls Testing

• Test programmer, thermostat, and zone valves
• Confirm the boiler fires up correctly from a thermostat call for heat
• Verify modulation is working correctly

9. Magnetic Filter Clean

If your system has a magnetic filter, the engineer should isolate, remove, clean, and refit it. Ask about having one fitted if you do not already — it protects the boiler and improves efficiency.

10. Service Record

At the end of the service, the engineer must complete a written service record noting any issues and recommendations. Keep this record safe — you will need it for warranty claims and when selling your home.

What Is NOT Usually Included

• Power flushing the central heating system
• Replacing parts (charged separately)
• Checking individual radiators or TRVs
• A landlord gas safety certificate (this is a separate document)

Book a Complete Boiler Service

Find a Gas Safe engineer who will carry out a thorough, documented service through Checkatrade or compare quotes via Leads2Trade.