I had the same issue with this receiver today, all i did was move the thermostat from one room to another. Changing the dip switches on the back made no difference (these only control the 5+2 or 7 day program and +.25 or +.5 degree increments) I opened up the thermostat and metered the battery connections on the board and they did not supply any voltage to the board, all I had to do was push down firmly where the solder terminals are and it worked straight away with no further issues. If that doesn't work it might need re-soldering which any halfwit can do (even me🙂
the red blinking light on receiver means they're not paired, so when the red light is blinking hold down the pairing button beneath the battery cover for 3 secs once the flashing red light goes solid red press the pair button again for 3 secs and enjoy 😛