Aprilaire 400 flashing on digital humidistat “Call for service”

Consumer question:

Aprilaire 400 flashing on digital humidistat "Call for service"

E3 flashing little manual plastic piece fell out when trying to move it. What does E3 mean dont want to call repair if not necessary.

Aprilaires’ response:

Thank you for contacting us regarding the E3 code.  The E3 code means there is an error in the terminals marked ODT in the control.  When the blue tag labeled "Manual Mode" fell out, it caused the control to show the error code.  The ODT terminal requires either the manual mode resistor (blue tag) or the outdoor temperature sensor or the E3 code will appear.

If the manual mode resistor still has the two wires coming out of it, you could simply put it back into the ODT terminals and reset the code by putting the control into the test/reset position with the furnace running.  If the wires are broken or missing, you would need a new one.  You can find a new resistor at a local Aprilaire dealer, or purchase on our estore by following the link below:


If you have any further questions regarding this or any of our products, please feel free to contact our customer service department at your earliest convenience.

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