digistat rf2 re-commissioning problem?

I have a digistat rf2 thermastat and have tried to re-commision it several times but to no avail. For some reason it is not communicating with the SCR unit.After going through the procedure the red led light on the scr unit is supposed to flash several times but it doesn't. I am having to put the heating on by using the over ride button which obviously means it's on constantly!.....please help!!