Drayton DigiStat 2 heating programmer issue

roytom2

My Drayton wireless room thermostat/programmer isn’t communicating with the receiver box by the boiler - the heating won’t come on.
But the receiver box isn’t showing the alarm (red) indicator (ie. receiver error) but is showing the green (receiving) light. 

I’ve turned both the room thermostat and receiver on and off but still it’s not instructing the boiler to come on. This problem happened occasionally last winter and I think taking the batteries out of the room thermostat seemed to reset things - although I could have been mistaken.
Now I’ve found that the capacitor in the receiver box very often fails but the symptom is the red warning light flashing - mine isn’t. This would have been an easy fix as the cap is on eBay quite cheaply.
Any ideas? I don’t particularly want to replace the room thermostat and receiver but if I did I’d want a better one that’s programmed via WiFi it possible.