My gas central heating hive send units is not connecting to the thermostat

[Sidsmith]

My British gas (hive) central heating sender unit is not connecting to the thermostat, the thermostat keeps saying no internet connection but I know working properly as I've just checked it's

[JimM1]

@Sidsmith Few different types of hive and thermostat's, but the hive site is also good for diagnostics off there equipment!