You try to trigger the rule, with a item which is never updated.
You also miss the item file. An example explaining the exec binding.
rule "termostato"
when
Item temperature_out received update
then
if ( Float.parseFloat( Temperaturen_out.state) > 24) {
LED.sendCommand(OFF)
}
end
Something like this. Not tested typed in my phone, may contain typos.
@warlock Edit:
Your thing looks good and the Eule gets triggered as you geht the logging.
Now parse string to float, the output value of exec is a string, which can not be compared to a number.
Can you toggle the led with a switch? Does the led work?
Removed triggeringItem since it works only with at least openhab 2.2.