DRAYTON Digistat +3RF loses contact to SCR controller unit?

My Drayton DigistatSCR unit looses boiler control. the green light stays on, but ,will not fire up boiler, the pulsing red light flashes once every 30 seconds, 3RF unit is comunicating and although flame sign is on, no SCR control. The way I reinstate the SCR unit totalk to stat unit is to switch off mains at SCR boiler unit, and ,switch on power again, after a time lag the Digistat SCR restarts comunication,red light flashes, and green light comes on and boiler lights. There is no sequence to this fault. I have brought the stat closer to the control unit, no change.