Drayton Digistat+2 RF?

Drayton Iflo Digistat +2 RF thermostat shows error E16 when powered up after fitting new batteries. I believe this is a thermostat error, but is it repairable or do I need a new unit? Plus, when I check for connection (power up after pressing the No.1 and No.2 buttons in sequence ) the red light flashes , so I believe I have connection, but I can't clear the error, any ideas please?