How to Service a Boiler UK — What a Gas Safe Engineer Does
A boiler service is a legal must for landlords, and a warranty requirement for most manufacturers. Here is exactly what a Gas Safe engineer does — and what a cowboy skips.
Step-by-step method
1. Visual check and flue inspection
Case off, check for corrosion, water marks, soot. Inspect flue joints for leaks — critical for CO safety.
2. Combustion analysis (flue gas)
FGA meter into flue. CO/CO2 ratio must be <0.004. Records go on your Gas Safe cert.
3. Check pressures
Gas working pressure at inlet (20mbar for natural gas), system water pressure (1.2 bar), gas rate at burner.
4. Seals and consumables
Replace burner door seal if squashed. Check condensate trap, clean if silty. Test PRV manually.
5. Report + Gas Safe record
Landlord Gas Safety Record (CP12) for rentals. Homeowner receives a service record for warranty and insurance.
Frequently asked questions
How much does a boiler service cost UK?+
£90–£140 for a homeowner. £110–£160 with a landlord CP12.
Do I need an annual service?+
Legally, only landlords. But every major manufacturer voids warranty without annual service records.