New smart radiator thermostat dead

Hi there.

Just bought a 4 set smart radiator thermostat to extend my home installation. 3 worked perfectly on set-up (even though the original batteries were very low on charge - shelf-life?) but the 4th one refuses to react when I put batteries in. Using recommended AA 1,5V batteries and nothing, no light, no movement, nada.

What could be wrong?

Answers