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