Why is my Potterton EP3002 control "fluttering"?

I have a Glow Worm wall mounted gas boiler & Potterton EP3002 digital control box, replaced about 18months ago. The 2 mains neons just "flutter" & you can hear the switch contacts rapidly trying to connect, but no amount of switching on & off and adjusting will get the unit functioning. The clock time is stuck at the time the fault occurred. I have taken the box off the mounting plate & fiddled around with what I can externally. But nothing but the fluttering contact noise. Is this familiar to anyone & can anything be done apart from replacing the control unit? Any help gratefully received!