The filter on my Aprilaire model 600 humidifier doesn’t seem to be filling with water. Nothing has changed since the last season and the setting is at 5.
If it is set at 5 that is equivalent to about 35% humidity. So if the current humidity level is higher than that it would not be running. An easy way to tell is to turn the unit to test reset (turn it past 7 and the humidifier on light should begin to blink with our 58-60 control) This should turn the humidifer on and it will run for approximately one minute. If this happens the unit is functioning normally and then when you turn it back to 5 it should come on , if the HVAC is running and the humidity falls below 35%.