It appears that the kasa ke100 radiator valve hasn't implemented the activeThermostatMode parameter in Google home. 

https://developers.home.google.com/cloud-to-cloud/traits/temperaturesetting

My assumption is that if the ambient temperature is less than the thermostats set temperature then activeThermostatMode would be set to heat or if the ambient temperature was great than thermostat's set temperature activeThermostatMode would be set to off. 

Has anyone found an alternative to using this parameter?

Is my assumption correct that this parameter would normally be set to either heat or off allowing for easy boiler state manipulation?

Has anyone been in touch with tp-link about this?