mypros+
Error code reference

Amana Microwave Error Code 21

Service code that displays repeatedly when room temperature may be too low.

Amana codesAmana microwave codes

Service code that displays repeatedly when room temperature may be too low.

First step from the service manual

Check that room temperature is not too low.

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

MyPros+ Max

Get the full diagnostic procedure for 21.

  • Step-by-step tests with expected resistance, voltage, and continuity values
  • Wiring diagram references and connector pinouts from the OEM service manual
  • Verified part numbers when replacement is required
Get the full procedure

$29/month · Cancel anytime · Or $9.95 3-day pass

What 21 means on a Amana microwave

Error code 21 on an Amana microwave is a service code triggered when the unit's internal temperature sensing circuit detects ambient or internal temperatures that fall below an acceptable operating threshold. The microwave's control board continuously monitors temperature conditions, and when readings drop too low, the unit displays this code as a protective and diagnostic signal. This is not an indication of a failed component in the typical sense, but rather a flag that environmental conditions are outside the range required for proper operation.

The most common scenario involves the microwave being installed or used in a space where room temperature has dropped significantly, such as a garage, unheated utility room, or during cold weather. Microwaves are generally designed to operate within a defined temperature range, and sustained exposure to cold environments can cause the temperature sensor or thermistor to report readings that the control board interprets as a fault condition.

In some cases, the code may also appear if the temperature sensor itself is malfunctioning and reporting inaccurately low readings even when the room is at a normal temperature. If the ambient environment is verified to be at a reasonable temperature and the code persists, the sensor or its wiring circuit may need to be inspected for faults, loose connections, or component failure.

Source: manufacturer service documentation.

Common causes of 21

  1. 01

    Low ambient room temperature

    Wiring / connection

    The most frequent cause is the microwave being located in a cold environment such as a garage or unheated room. Check the room temperature and ensure it is within the normal operating range before further diagnosis.

  2. 02

    Temporary cold exposure during transport or installation

    Wiring / connection

    If the microwave was recently moved from a cold environment, the unit may display code 21 until it warms up to room temperature. Allow the appliance to acclimate for 30 to 60 minutes in a heated space.

  3. 03

    Faulty temperature sensor or thermistor

    Part replacement

    If the room temperature is normal and the code persists, the internal temperature sensor may be reading incorrectly due to component failure. This would require testing and likely replacing the sensor.

  4. 04

    Loose or damaged sensor wiring

    Wiring / connection

    A loose connection or damaged wire leading to the temperature sensor can cause inaccurate readings that trigger code 21. Inspecting the wiring harness connected to the sensor may reveal the issue.

  5. 05

    Control board fault

    Part replacement

    In rare cases, the control board itself may be misinterpreting temperature sensor data due to an internal fault. This is typically the last item to suspect after ruling out environmental and sensor issues.

See the test procedure for each cause

Frequently asked questions about 21

What does 21 mean on a Amana microwave?
Code 21 is a service code indicating that the microwave has detected a temperature condition that is too low for normal operation. It is typically triggered by cold ambient room temperatures rather than a mechanical failure. The unit's control board monitors temperature and displays this code as a warning when readings fall below the acceptable threshold.
How do I fix error code 21 on my Amana microwave?
Start by checking the temperature of the room where the microwave is located. If the space is cold, move the microwave to a warmer area or heat the room and allow the unit to acclimate for at least 30 to 60 minutes. If the code persists in a normal-temperature environment, the temperature sensor or its wiring should be inspected for faults.
Is it safe to use my Amana microwave when code 21 is showing?
Code 21 indicates the microwave is operating outside its recommended temperature range, so it is best to avoid using the unit until the issue is resolved. Operating in very cold conditions can affect performance and potentially cause other issues. Address the temperature condition first before resuming normal use.
Will resetting my Amana microwave clear error code 21?
A simple reset by unplugging the microwave for a few minutes may temporarily clear the display, but the code will return if the underlying condition, such as low room temperature or a faulty sensor, has not been corrected. Addressing the root cause is necessary for a lasting fix.
How much does it cost to repair error code 21 on an Amana microwave?
If the issue is simply a cold room, there is no repair cost involved. If a temperature sensor needs to be replaced, parts and labor costs can range from around $75 to $200 depending on the specific sensor and service rates in your area. A control board replacement, if required, would typically be at the higher end of the cost range or may make repair less economical depending on the age of the unit.

Related Amana microwave codes

All Amana microwave codes
View all 43 Amana microwave codes

78,000+ service manuals · 160,000+ error codes · 55+ brands

Get Started

$29/month · Cancel anytime · Or $9.95 3-day pass