This display indicates a temporary hold on the burner. There is a demand on the boiler from the DHW circuit for heat, the pump is powered on, but the boiler supply sensor indicates that the water temperature is too high to ignite. This is a temporary hold on the burner only and all other functions will remain functioning properly.
This error will clear itself when either the boiler supply temperature drops below the BOILER SUPPLY minus boiler supply differential (5ºF) or DHW SETPOINT is satisfied and no longer calls for heat.