Error Code Resources
Quest dehumidifiers display error codes to help you quickly identify what’s happening with your unit. Most codes are informational — your unit has detected a condition outside its operating range and will restart automatically when conditions improve. Others indicate a component issue that may need attention.
Use the guide on the right to find your code, understand what it means, and follow the recommended steps. If you work through the diagnostic and need to submit a warranty claim or order parts contact our support team with your findings and serial number ready.
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If you aren’t sure of the next steps, our team can help.
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E1 RH sensor Error
What’s happening
The E1 code triggers when the control cannot communicate with the RH sensor. This could cause the unit not to control humidity to the setpoint.
Step-by-step diagnostic
Check if sensor is unplugged at sensor or control board
Check sensor and wire for damage
Replace sensor to see if issue resolves
What the REsults Mean
➔
Reconnect sensor is unplugged
➔
Replace the sensor if damaged
➔
Replace the sensor first if E1 code persists.
➔
Replace the power board if Sensor did not resolve
e2 Low dew point
✓ This is not a malfunction. The unit is protecting itself and will restart automatically when conditions improve.
What’s happening
Dew point measures the actual amount of moisture in the air. When it drops below 40°F, there isn’t enough water in the air for any dehumidifier to work — even if your humidity gauge reads high. The unit shuts off automatically and will restart when the dew point rises above 40°F.
Step by Step Diagnostic
No correction needed. Ignore the RH% reading until the dew point increases.
If you need to reduce RH% now, heat the space — this will lower the RH%. If the temp cannot be raised a desiccant dehumidifier may be needed.
E3 Evaporator Not Cooling
ⓘ Also displayed as “03” on some models.
What’s happening
The E3 code triggers when the evaporator doesn’t cool down enough, which can be caused by several things — from something as simple as a dirty filter to a fan, capacitor, or refrigerant issue.
Step-by-step diagnostic
Power cycle the unit to reset the code, then turn it back on.
Verify the fan comes on and there is good airflow through the unit. Check and replace the filter if dirty.
Verify the compressor starts within 2 minutes of power-on.
Run for 10 minutes. Look for: 10–25°F temperature rise from intake to exhaust, and the compressor suction line or evaporator becoming cold.
What the REsults Mean
➔
Fan doesn’t come on
Likely a bad fan, fan capacitor, or power board.
➔
Fan runs but poor airflow
Dirty filter or restricted ductwork.
➔
Compressor doesn’t start
Bad relay, capacitor, power board, or compressor.
➔
Compressor runs, coil gets cold
Likely a bad temperature sensor or sensor in wrong location.
➔
Compressor runs, coil stays warm
Likely low refrigerant from a leak.
E4 Float switch error
What’s happening
The E4 code triggers when the control senses a change in the float terminals. Typically an external float switch has opened indicating to the control to shut the unit down. Removing the terminal block or float jumper will also cause this.
Step-by-step diagnostic
Reinstall terminal block if removed
If no float switch is installed make sure jumper is installed between both float terminals.
Check external float switch and wires for damage.
What the REsults Mean
➔
An open circuit between the float terminals triggers the E1 code. Closing the circuit using the above steps will resolve the code.
E5 Evaporator temp sensor error
What’s happening
The E5 code triggers when the control cannot communicate with the Evaporator sensor. This will cause the defrost light to be on and the unit not to operate.
Step-by-step diagnostic
Check if sensor is unplugged at control board
Check sensor and wire for damage
If no issue is found, replace sensor to see if issue resolves
What the REsults Mean
➔
Sensor is bad
E6 Too hot
✓ This is not a malfunction. The unit will restart automatically once the temperature drops below 120°F.
What’s happening
The ambient temperature has exceeded the unit’s operating range. It shuts down to prevent unnecessary running and will automatically restart when the room cools down.
What to do
No correction needed. Wait for the temperature to drop below 120°F.
If this happens frequently, consider improving ventilation or cooling in the space.
If the air temp is actually under 120F but getting this code the intake temp/humidity sensor may be bad.
E7 Too Cold
✓ This is not a malfunction. The unit will restart automatically once the temperature rises above 40°F.
What’s happening
The ambient temperature has dropped below the unit’s operating range. It shuts down to prevent ineffective or damaging operation and will automatically restart when conditions warm up.
Step by Step Diagnostic
No correction needed. Wait for the temperature to rise above 40°F.
If the space regularly drops this low, consider whether a different unit or insulation is appropriate for your setup.
If the air temp is actually above 40F but getting this code the intake temp/humidity sensor may be bad.
E8 Control communication Error
What’s happening
The E8 error code presents when the Display board and power board cannot communicate with each other.
Step by Step Diagnostic
Check to see if the communication cable is unplugged or damaged.
Unplug and reconnect communication cable on both sides.
Replace Display Board
Replace power board
What the REsults Mean
➔
Damaged or unplugged cable will prevent communication.
➔
Communication cable may have not been seated will in connector.
➔
Bad display board
➔
Bad power board
E9 High Pressure safety
What’s happening
The E9 code presents when the pressure in the refrigeration is to high. Low airflow is the most common cause.
Step by Step Diagnostic
Check air filter and replace if needed
Check blower function and replace in needed
Check and resolve any other air restrictions
What the REsults Mean
➔
Air filter clogged causing lack of airflow. This drives up the refrigerant pressure
➔
Blower may not be working causing lack of airflow
➔
Other air restrictions like poor ducting or blocked intake/exhaust
➔
Bad power board
E11 Refrigerant leak sensor
What’s happening
The E11 code is presents when the refrigerant sensor sees a concentration of refrigerant. This could be due to a leak of refrigerant from the machine.
Step by Step Diagnostic
Check the refrigerant sensor. Could be unplugged or damaged.
Check for refrigerant leaks from the machine.
Check for any combustible gas from other sources. Natural Gas, Propane or refrigerant from other equipment.
Replace the sensor
What the REsults Mean
➔
Sensor being damaged or unplugged could trigger the sensor to incorrectly indicate a leak.
➔
A leak in the refrigeration system is present.
➔
Sensor can pickup on leaks from other sources not just the machine it is in.
➔
Sensor could just be bad indicating a leak when not present.
E12 Power supply issue
What’s happening
The E12 code is triggered when the Phase monitor sees a problem with the incoming power to the machine. Commonly this is just a simple phase rotation issue but could be a power imbalance.