IDEAL HE24 NOT WORKING?

I HAVE THE ABOVE UNIT WHICH WAS SERVICED 2 MONTHS AGO AND JUST NOTICED NO HOT WATER OR HEATING, ON CHECKING THE UNIT THE DISPLAY IS BLANK
THERE IS POWER GETTING THROUGH FROM THE TIME CLOCK TO THE UNIT . THE FUSE ON THE CONTROL BOARD IS FINE . PLEASE CAN YOU ADVISE IF POSSIBLE OF WHAT COULD CAUSE THIS OR HOW TO FIX