JennAir JMV Code E21: thermal sensor circuit open

What E21 means

E21 appears on JennAir over-the-range microwave hoods, including the JMV9196CS and the JMV8000 series. The control board sees the thermal sensor circuit as open, as if the sensor wire were cut or unplugged. The official guidance names the thermal sensor, the appliance control board and the wiring between them. Owners see E21 and the microwave stops heating or will not start a cycle.

Common causes of E21

Thermal sensor has failed open
Wire or connector to the sensor is loose or broken
Appliance control board is misreading the sensor circuit

✓ One safe check you can try

1. Press Stop/Cancel and open the door for a few minutes so the cavity cools. 2. Make sure the vent slots on the front and top are free of grease and the unit is not boxed in. 3. Close the door and try a short 30-second run with a cup of water inside. 4. If E21 returns right away, stop using the microwave and book a visit.

! Why to stop there

An open sensor circuit can only be confirmed with a meter reading on the sensor and its harness.
Opening the hood puts you near the high-voltage section, which keeps charge after unplugging.
If the real problem is the board, replacing the sensor alone leaves the code on screen.
We give a written price first and stand behind the repair for 30 days.

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.

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Other Microwave codes

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E21E21 questions

What does an open thermal sensor circuit mean in plain words?

The control expects a steady reading from the sensor and instead finds no connection at all. It is similar to a thermometer with a snapped lead. The microwave then refuses to heat rather than guess the cavity temperature.

Could E21 go away on its own?

It can if a connector was only slightly loose, but then it usually returns during the next heavy use. A code that clears for a day and comes back still needs the sensor circuit checked.

How does E21 compare with E22?

They point at the same sensor but report opposite conditions. E21 reports the circuit open, while E22 reports it shorted. We read the actual sensor values to see which one we are dealing with.