E21 Compressor error - locked rotor

serious

The Bosch E21 error code on your refrigerator indicates: Compressor error - locked rotor. This typically requires troubleshooting the compressor system.

Bosch Refrigerator Affects 1 model

What Causes Error E21

high likelihood #1

Compressor overload/overheating

The compressor has overheated due to dirty condenser coils, poor ventilation, or the overload protector has tripped.

high likelihood #2

Start relay failure

The relay/start device that kicks the compressor motor into action has burned out.

medium likelihood #3

Compressor motor failure

The internal motor windings in the compressor have failed.

medium likelihood #4

Low refrigerant (sealed system leak)

A refrigerant leak has caused the compressor to run improperly and trigger protection circuits.

How to Fix Error E21

  1. Step 1: Unplug and wait 15 minutes

    Compressors have thermal overload protection that needs time to cool down and reset.

  2. Step 2: Clean the condenser coils

    Pull the fridge away from the wall. Find the condenser coils (usually on the back or underneath). Vacuum or brush off all dust and pet hair. Dirty coils cause overheating.

    ⚠️ Condenser coils may have sharp edges.

  3. Step 3: Ensure proper ventilation

    Make sure there's at least 1 inch of clearance on all sides and top of the refrigerator for air circulation. Fridges crammed into tight spaces overheat.

  4. Step 4: Check the start relay

    The start relay is a small device plugged into the side of the compressor (usually at the back bottom of the fridge). Unplug it and shake it — if it rattles, it's failed. Also smell it for burning.

    ⚠️ Unplug the refrigerator first.

  5. Step 5: Replace the start relay

    If the relay rattles or smells burnt, replace it. This is a cheap, easy fix — it just unplugs from the compressor and the new one plugs in the same way.

  6. Step 6: Listen to the compressor

    After relay replacement, plug in the fridge. You should hear the compressor hum steadily. Clicking on/off every few seconds means the compressor itself may be failing.

Parts You Might Need

If troubleshooting doesn't resolve error E21, you may need to replace one of these parts:

Compressor Start Relay

other $10-$30
Find on Amazon PartSelect

Start Capacitor

other $8-$20
Find on Amazon PartSelect

Condenser Coil Brush

other $8-$12
Find on Amazon PartSelect

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When to Call a Professional

If the compressor clicks on and off repeatedly, if you suspect a refrigerant leak, or if the start relay replacement doesn't help

  • Compressor replacement is a major sealed-system repair requiring EPA certification
  • Refrigerant handling requires specialized equipment and certification
  • A failed compressor may mean it's more economical to replace the entire appliance

Video Repair Guides

Watch a repair walkthrough for this error code on YouTube:

▶ Search YouTube for "Bosch refrigerator error E21 fix"

Models Affected

This error code has been reported on the following Bosch refrigerator models:

B36CL80SNS