FER FALCON II HEATING NOT WORKING?

When I switch the on/off/reset switch to the "on" position, the clock on the front is stuck with all segments of the LCD display visible i.e. all the symbols and the main clock shows 88:88.

I think this appears to be preventing the central heating coming on when I try to do so, although the hot water works fine and as normal.

I have tried the small reset button with a pencil, however the display remains the same.

I have also briefly turned the on/off/reset switch to the reset position and this also has no effect, as has switching the wall switch off and on briefly.

Any help would be greatly appreciated as this is the coldest night here for a while!

Cheers
Mike