How hvac_action is calculated if my ubderlying device doesn't expose one ?

[jmcollin78]

Good question....

For devices that do not have an hvac_action, I simulate one:

For over_valve, the valve opening must be > min,
for over_climate, it's like you said, the difference between the target and the current temp must be > 0 (or < 0 in Cooling mode).
And be careful with multi-devices Vtherm, at least the underlying must be its hvac_action (simulated or not) so that its hvac_action is ‹ on ›.

For over_switches, at least one of the controlled switches must be 'on'.

So indeed you can see differences compared to the actual ignition state.
The ideal would be to have an hvac_action attribute calculated according to the real state of the device (if it has one or if you can simulate one of course).