Aprilaire dehumidifier humidity sensor
Relevant for E1 sensor faults after checking the connector and board pins for corrosion.
$35-$140
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Aprilaire Dehumidifier Error Codes — Quick Reference
Aprilaire whole-home dehumidifiers (Models 1700, 1710, 1750, 1850, E100) display fault codes on the digital control panel. These dehumidifiers are typically installed in the ductwork or as stand-alone basement units. Fault codes indicate sensor failures, drainage issues, refrigeration problems, or control board faults.
| Code | Meaning | Quick Fix |
|---|---|---|
| E1 | Humidity sensor fault | Check sensor wiring; replace sensor |
| E2 | Inlet temperature sensor fault | Inspect NTC sensor; check connections |
| E3 | Outlet temperature sensor fault | Check coil sensor wiring |
| E4 | High-temperature protection activated | Check airflow; clean filter/coils |
| E5 | Defrost cycle active | Normal during cold conditions — wait |
| E6 | Refrigeration fault / compressor issue | Check refrigerant; call HVAC tech |
| E7 | Fan motor fault | Verify fan motor spins; check capacitor |
| E8 | Full bucket / drain blocked | Empty tank; check condensate drain |
| E9 | Float switch fault | Check float switch and drain line |
| Er | General control error | Power-cycle unit; check board |
Need Replacement Parts?
Before ordering, match the HVAC part to the model number, electrical rating, and failure symptom. Check current prices on Amazon - prices and availability change frequently.
Most Common Faults
E1 — Humidity Sensor Fault
The built-in humidity sensor (humidistat) has failed or is reading outside normal parameters. First, inspect the sensor connections on the control board — corrosion on pins is common in damp basement environments. If the sensor is a plug-in module, try reseating it. A failed humidity sensor will need to be replaced; Aprilaire sells replacement sensor modules for most models.
E4 — High-Temperature Protection
The unit sensed that internal temperatures exceeded safe limits. This is almost always caused by restricted airflow. Check the air filter — Aprilaire dehumidifiers have a washable filter that requires monthly cleaning in high-humidity environments. Also check that the inlet and outlet vents are not blocked by boxes, insulation, or stored items.
E5 — Defrost Cycle
In temperatures below 65°F, the dehumidifier’s coils will frost over. E5 indicates the unit has entered its automatic defrost cycle — this is normal operation, not a fault. The unit will temporarily stop dehumidifying and run the fan to defrost the coils. If E5 appears constantly in warm conditions, the refrigerant charge may be low.
E6 — Refrigeration / Compressor Fault
A serious fault indicating the compressor is not running, refrigerant pressure is abnormal, or the compressor thermal protection has tripped. Check that the unit has been running in ambient temperatures above 50°F (compressors will not start below this). If the fault appears in normal conditions, the unit needs refrigerant diagnosis by a certified technician.
E8 — Full Bucket / Drain Blocked
For units with a gravity drain, check that the condensate hose is not kinked, clogged, or running uphill. For units with internal buckets, empty the bucket and inspect the float switch. The float switch stem can sometimes stick in the “full” position if the bucket was left full for an extended period.
E7 — Fan Motor Fault
The evaporator fan motor has stopped or is drawing abnormal current. Check that nothing is obstructing the fan wheel. On older units, the fan motor capacitor can fail, preventing the motor from starting. Test the capacitor with a capacitor meter — Aprilaire dehumidifier fan motors typically use a 5–10 µF run capacitor.
Model-Specific Notes
- Model 1700/1710 — 70-pint capacity, duct-mounted or stand-alone, uses E-series error codes
- Model 1750 — 95-pint, similar fault code structure; adds E9 float switch monitoring
- Model 1850 — 95-pint with Wi-Fi control; same codes, accessible via Aprilaire app
- Model E100 — Energy Star rated; displays codes on front LED panel
When to Call a Pro
E6 (refrigeration fault) always requires a certified HVAC/R technician — this involves refrigerant handling and specialized pressure gauges. E7 fan motor faults also require a technician if motor replacement is needed.