Trying to service a GeneralAire 1040 furnace humidifer

I am not getting water flow through the solenoid on my GeneralAire 1040 power humidifer. I assume this means that either the solenoid or the humidistat are responsible. (I remember a heating/A/C friend of mine once telling me that humidistats don't have a long lifespan.) I started to unscrew the water inlet side and started getting dripping, so I am assuming that the water flow is OK. (I don't know for sure if it is at the right pressure, though.)
How can I determine whether the solenoid needs to be replaced (or cleaned) or if it is the humidistat?
I have a multimeter and so can do any voltage/amp/continuity tests, but don't know what to look for. (E.g., I don't know if there is supposed to be continuity through the solenoid only when it is on or off or both.) The humidistat is just a break in a circuit that includes the solenoid and the furnace (blower?).
Any help is much appreciated!
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Gotta be the thermostat....
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