Maytag Washer Error Code F40

F40 means the washer has detected that the ATC (Automatic Temperature Control) thermistor is either open or shorted. This thermistor is responsible for measuring water temperature so the machine can blend hot and cold water accurately. The control board identified a resistance reading outside the acceptable range and triggered the fault code. The washer will need the thermistor, wiring, and connections inspected to find the cause.

Running the washer with an active F40 code is not recommended. Without a functioning ATC thermistor, the control board cannot accurately regulate water temperature, which can result in clothes being washed at unintended temperatures. Continuing to run the washer may also mask additional issues if the wiring fault worsens. It is best to diagnose and resolve the fault before resuming normal use.

A reset may temporarily clear the F40 code from the display, but it will return if the underlying fault with the ATC thermistor or its wiring has not been corrected. Resetting without repairing gives no information about whether the problem is resolved. The proper approach is to perform the TEST #5 diagnostic procedure to identify and fix the actual cause, after which the code should clear and not return.

Some causes of F40 are DIY-friendly, such as reseating a loose connector or inspecting the wiring harness for visible damage. However, if the thermistor itself has failed, it will need to be replaced, which requires locating the correct part and accessing internal washer components. Following the diagnostic procedure in TEST #5 is the recommended starting point to determine what specifically has failed before ordering any parts.

Repair costs vary depending on the root cause. If the fix is simply reseating a connector, there is no parts cost. A replacement ATC thermistor typically costs in the range of $15 to $50 for the part alone. If the control board needs to be replaced, costs can range from $100 to $300 or more for the part. Adding professional labor generally brings the total repair cost to somewhere between $100 and $400 depending on the fault.