Danfoss rx1 thermostat shows 'of' ?

Remove batteries from room stat,turn off the electrical supply to reciever unit.
Turn back on the electric to reciever unit,the red light should be on,press the top "manual" button,the green light should come on and boiler should fire (assuming the programmer is in an "on" period)
Press the bottom button,and keep it pressed,then press the top button until the green light flashes,stand about 6 feet away,and refit the batteries to the stat while observing the reciever unit,either the red or green light (cant remember which) should flash to show the 2 units are syncronised.

Another basic test if all seems ok,when turning the stat up or down,when the green light on the reciever unit comes on or goes off,its usually accompanied by an audible "click" ive found,that if this is not happening, the reciever unit does not switch either on or off,may be intermittant.
Replacement is the only cure.
garden led light