After more time on the phone to Hive this evening here’s the definitive guide on re-pairing the boiler module (as is it’s technical name!) should it go offline.

1/ Hold the “Central Heating” button until the boiler module flashes pink.

2/ Hold the “Central Heating” button until the boilder module flashes yellow.

3/ Hold the “Back” and “Module” buttons down until a countdown starts. Continue holding until the countdown completes. This will factory reset the thermostat/boiler module.

The boiler module should then pair. This will reset your schedules and you will need to set them up again.