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Error code reference

Amana Microwave Error Code E21

Thermal sensor open error.

Amana codesAmana microwave codes

Thermal sensor open error.

First step from the service manual

Check sensor connection, wiring, or PCB.

The complete diagnostic procedure includes additional test steps, resistance specifications, wiring diagram references, and component test points.

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  • Step-by-step tests with expected resistance, voltage, and continuity values
  • Wiring diagram references and connector pinouts from the OEM service manual
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What E21 means on a Amana microwave

The E21 error code on an Amana microwave indicates a thermal sensor open circuit fault. The thermal sensor, sometimes called a cavity temperature sensor or thermistor, is responsible for monitoring the internal temperature of the microwave cavity during operation. When the control board detects that the sensor circuit is open rather than returning a valid resistance signal, it triggers the E21 code and halts operation to prevent potential overheating damage.

An open circuit in the sensor loop can result from a physically broken sensor element, a disconnected or corroded wiring harness connector, or damaged wiring between the sensor and the PCB. The thermal sensor typically operates by changing resistance in response to temperature, and the PCB reads that resistance to regulate cooking cycles. When the circuit is open, no resistance reading is possible, which the board interprets as a fault condition.

The first diagnostic step is to inspect the sensor's wiring harness connection at both the sensor itself and at the PCB. Check for loose, burnt, or corroded connector pins. If the connections are secure, use a multimeter to test the sensor for continuity. A reading of infinite resistance confirms the sensor element is open and the component requires replacement. If the sensor tests properly, trace the wiring for breaks or chafing before suspecting a faulty PCB.

Source: manufacturer service documentation.

Common causes of E21

  1. 01

    Disconnected sensor connector

    Wiring / connection

    The wiring harness plug connecting the thermal sensor to the PCB can work loose over time, especially after cleaning or servicing. Inspect both ends of the connector for a secure, fully seated connection.

  2. 02

    Failed thermal sensor

    Part replacement

    The sensor element itself can fail internally, creating an open circuit. Testing with a multimeter will show infinite resistance across the sensor terminals, confirming it needs replacement.

  3. 03

    Damaged or broken wiring

    Part replacement

    The wires running between the thermal sensor and the PCB can become chafed, pinched, or broken, interrupting the circuit. Visually inspect the full wire run for any visible damage or burnt insulation.

  4. 04

    Corroded or burnt connector pins

    Wiring / connection

    High heat or moisture inside the microwave cavity can cause connector pins to corrode or burn, increasing resistance to the point of an open circuit. Check the connector pins carefully for discoloration or corrosion.

  5. 05

    Faulty PCB

    Part replacement

    If the sensor and all wiring test correctly, the control board's sensor input circuit may have failed. This is the least common cause and should only be suspected after ruling out the sensor and wiring.

See the test procedure for each cause

Frequently asked questions about E21

What does E21 mean on a Amana microwave?
E21 indicates a thermal sensor open circuit error. The microwave's control board is not receiving a valid signal from the cavity temperature sensor, which suggests the sensor itself, its wiring, or the connection to the PCB has failed. The microwave shuts down to prevent unsafe operation without temperature monitoring.
Can I fix an E21 error myself?
Some causes are DIY-friendly, such as reseating a loose connector or inspecting wiring for visible damage. However, working inside a microwave involves high-voltage components, including the capacitor, which can retain a lethal charge even when unplugged. If you are not experienced with high-voltage appliance repair, this job is best left to a qualified technician.
Is it safe to use my Amana microwave while E21 is displayed?
No. The E21 code causes the microwave to stop operating specifically because it cannot monitor internal temperature. Continuing to use it without a functioning thermal sensor could result in overheating or damage to internal components. The microwave should remain out of service until the fault is diagnosed and repaired.
Will resetting the microwave clear the E21 error?
Unplugging the microwave for a short time may temporarily clear the error, but it will return as soon as the control board detects the open sensor circuit again during startup or operation. A reset does not fix the underlying hardware fault, so the sensor, wiring, and connections must be inspected and repaired.
How much does it cost to repair an E21 error on an Amana microwave?
Repair costs vary depending on the root cause. A replacement thermal sensor typically runs in the range of $10 to $40 for the part alone. If a new control board is needed, parts can range from $80 to $200 or more. Adding professional labor, total repair costs generally fall between $75 and $250 depending on what components require replacement.

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