Your boiler has detected an unsafe level of carbon monoxide or improper combustion, which means it has shut down to protect your safety.

Combustion fault/high CO

What causes this fault?

This fault occurs when the boiler's internal sensors detect that the fuel is not burning safely or that dangerous carbon monoxide levels are present within the unit. The most common reasons include a failing gas valve that isn't regulation pressure correctly or worn-out ignition components that are preventing a clean flame.