KitchenAid Over-the-Range Microwave Code E21: thermal sensor or control board

What E21 means

On KitchenAid over-the-range microwaves, including the KMHS120ESS and KHMS155LSS, E21 indicates a possible problem with the thermal sensor, the appliance control board, or the associated wiring. The thermal sensor reports temperature so the microwave can protect itself. Without that reading the microwave may refuse to heat, and the code stays on the display.

Common causes of E21

Thermal sensor reading out of range
Appliance control board problem
Wiring between sensor and board loose

✓ One safe check you can try

1. Press Cancel and let the microwave cool for ten minutes with the door open. 2. Make sure the vent area above and below the microwave is clear. 3. Unplug it for a minute, then plug it back in. 4. Try a short timed run with water. 5. If E21 stays, call us.

! Why to stop there

Three possible causes need meter testing
Replacing the board when a sensor is bad is an expensive mistake
You see the price in writing before work, and the work carries 30 days of warranty

Opening a panel yourself does not automatically cancel a manufacturer warranty, but it can cause accidental damage, and some manufacturers set their own service conditions. Check your warranty terms, or ask us, before deciding.

→Same appliance

Other Microwave codes

Probe or Insert ProbeKitchenAid Combination Microwave Message "Probe" or "Insert Probe": Seat the meat probe in its jack PUSH or PSHKitchenAid Built-In Microwave Message PUSH or PSH: The oven is waiting for Start Registration ErrorKitchenAid Over-the-Range Microwave Message "Registration Error": Check the home network and try again Sabbath, Sab, 5Ab, or 5A6KitchenAid Built-In Microwave Display Sabbath, Sab, 5Ab or 5A6: Sabbath Mode is on SEKitchenAid Over-the-Range Microwave Code SE: Keypad or user interface problem F4 E6KitchenAid Combination Microwave Code F4 E6: Wave guide temperature sensor reading is off F8 E5KitchenAid Built-In Microwave Code F8 E5: Fan air temperature sensor reading lost Locked, Lock or LocKitchenAid Built-In Microwave Message Locked, Lock or Loc: Unlock the control and door

E21E21 questions

What triggers a thermal sensor code?

The sensor sends a temperature reading that is out of range, or none at all. The control then stops heating to protect the unit.

Does a blocked vent matter?

It can contribute to overheating and should be cleared, but the code itself points to the sensor, board or wiring.

Do E21 and E22 need separate repairs?

They share the same official wording and sit in the same family. The digit tells the technician which reading tripped.