Potterton Ep3000 timer not working?

I have a Potterton EP3000 and the CH & HW in airing cupboard & the switches no longer seem to be working. Display is working. I pull them all the way down as and when I want HW & CH and can usually hear the function as water/heating is turned on, but it seems to be dead. Small flame in downstairs boiler but not firing up full. What do I need to do to fix it?