Eberspacher 701 problem

[airhoguk]

Evening I have a eberspacher diesel heater with a 701 timer/programmer. I went to run up the heating this afternoon using the instant heat button and the display went blank then came back to the normal time display. I was able to change the clock with no issues but when I pressed the heat button again blank display again.I’ve looked online and can’t find any similar issue so wondered whether anyone here had seen a similar problem? Many thanks
Sorry forgot to mention it ran fine two weeks ago on a program and battery is fully charged