It sounds like an intermittent fault with the relay of the wireless receiver, when calling for heat from the room thermostat.
You need to check for mains voltage coming out of the unit (the power comes out of terminal 3), I have had this on numerous occasions recently.
Test when it's working and they'll be mains voltage, when it doesn't work, they'll be no voltage even though the green light is lit.
Carefree
December 2010