Most likely you have crud buildup in the solenoid valve. But first make sure that you test accross the solenoid connections for voltage when the furnace is OFF. Put your meter to AC volts and see if you see 24 Volts when furnace is ON and 0 Volts when furnace is OFF. If you get those readings then you need to replace your solenoid valve. Available from mfg for about $55-60 or on ebay for about $40 shipped. search for Aprilaire 4040 Solenoid
If the above tests fail, you will need to ensure that the wiring is correct and not shorted, but is probably your valve. Install a fridge water filter in the water line to help prevent this in the future.
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Most likely you have crud buildup in the solenoid valve. But first make sure that you test accross the solenoid connections for voltage when the furnace is OFF. Put your meter to AC volts and see if you see 24 Volts when furnace is ON and 0 Volts when furnace is OFF. If you get those readings then you need to replace your solenoid valve.
Available from mfg for about $55-60
or on ebay for about $40 shipped.
search for Aprilaire 4040 Solenoid
If the above tests fail, you will need to ensure that the wiring is correct and not shorted, but is probably your valve. Install a fridge water filter in the water line to help prevent this in the future.