I have the exact same fault. Boiler engineer out 3 times and it seems to work just before he arrives.
Heard on the grape vine that the Drayton rf1 system is terrible anyway, i.e. engineer says he's had to change loads of them.
What i found out:
1. its not the damn batteries (whole heating system is less than 6 months old)
2. its not the wireless router interfering (would be stupid to design a transmitter and receiver that could be buggered by modern technology)
3. its not due to being on a gas meter and being in the emergency credit (sometimes it does work in this situation)
Conclusion: it is because the Drayton rf1 is totally sh1t.
Replace it, problem solved.
g.rawlins
February 2010