Boiler shows A04, flue gas safety device intervention, boiler shuts down.

Safety Warning

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, Faulty flue thermostat, Incorrect flue installation, Recirculation of combustion products

How to Fix / Troubleshooting

Safety: Do not attempt to operate the boiler with a suspected flue fault. Risk of carbon monoxide poisoning. Ventilate the area and contact a qualified engineer.

External check: Ensure the flue terminal is not blocked or covered.
Engineer inspection: A technician should check the flue thermostat, flue integrity, and combustion. Replace the flue thermostat if faulty and rectify any flue installation issues.
Reset: After the cause is removed and the boiler has cooled, reset the boiler and verify safe operation with a flue gas analyser.

Repair Difficulty

Professional Required 5/5

Required Part

Flue Safety Thermostat

Check Price on Amazon

We may earn a commission from links on this page.