I've been troubleshooting my humidifier for a bit now (just learning this stuff as I go). It would appear the wiring for the furnace (apparently the transformer) meets the wiring for the humidistat and the solenoid inside the furnace. I've replaced the solenoid already as we have hard water and it's pretty easy to replace.
What I'm seeing is that when I pull the new solenoid out of the wiring junction, I get a solid 28v at the wiring junction. When I put the solenoid back in, I get nothing. That doesn't make sense to me. If they are all wired together, where's the voltage going?