This morning I finally found some time to do some "sanity testing"
I shorted the two contacts on the old humidistat with a screwdriver and soon as I did that I heard a sound coming from the humidifier that sounded like air going through a pipe, which I presume actually meant that it opened flow of water and turned it on. Make sense, right, except at that moment the furnace itself was not running, i.e. the room temperature was at the level set by the thermostat. Is that right?
If that's correct and I just need to replace the humidistat, other than flipping the breaker turning off the furnace, should I turn off or disconnect anything else?