Boiler shows A09, flue gas over-temperature or flue sensor fault (on models fitted)

This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.

If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.

Possible Causes

Blocked flue, Incorrect flue length, Faulty flue temperature sensor, Poor combustion

Safety first: Turn off the boiler and do not use it until checked. Risk of flue gas spillage.

External flue check: Ensure terminal is clear.
Engineer tasks:
- Test flue gas temperature sensor.
- Inspect flue for blockages or incorrect installation.
- Perform combustion analysis and adjust gas valve if needed.

Flue gas faults must be handled by a Gas Safe engineer.

Professional Required 5/5

Flue Gas Temperature Sensor

Check Price on Amazon

We may earn a commission from links on this page.