I have a nest thermostat but also TRVs on every radiator.
The nest thermostat has its own temp sensor that is made redundant by the fact that each of the TRVs have their own temp sensor, so I need to create a helper entity for my automation to check if ANY of my TRVs hvac_action is set to heating. This should be the only state that makes the nest thermostat come on, if they're idle, it should turn off.