Your boiler has been left in a manual testing mode after a service or inspection and needs to be switched back to its normal operating setting.

Service mode switch in min position.

What causes this fault?

This issue occurs when a technician accidentally leaves a physical switch on the internal control board set to 'minimum' after performing a service or safety check. Because the boiler is being told to stay at its lowest power setting for testing purposes, it cannot respond to your thermostat's request for full heat. It is a simple human error where a manual override was not deactivated before the boiler casing was put back on.