F56 Safety switch-off — CO limit exceeded

What does F56 mean?

The boiler has safely shut off because the CO (Carbon Monoxide) limit has been exceeded. This indicates a defect in the combustion regulation or a contact fault at the gas valve.

• A component in the combustion regulation is defective
• Contact fault at the gas valve (plug not plugged in correctly or not plugged in, plug defective, slot is defective (loose connection))
• The gas valve is defective

Click steps to track your progress.

1. 1

   Check standing and working gas pressures (requires specialist tools).

2. 2

   Take combustion readings (requires specialist tools).

3. 3

   Check the filter on the inlet of the gas valve to ensure it is not blocked.

4. 4

   Check the resistance on the gas valve (refer to voltage sheet, requires specialist tools).

5. 5

   Check the continuity of the cable harness to the gas valve (requires specialist tools).