Drayton Digistat+2 RF heating system?

I am puzzled because while there does not seem to be an obvious problem with our system and all lights and displays look fine, there is no heat coming through. For a couple of weeks there has been heat but only in the mornings. I have followed the instructions in the online manual to change the timings but whatever I do it doesn't seem to make any difference. Has anyone any suggestions - I'd be very grateful for advice.