Carel E422

What does Carel E422 mean?

E422 on Carel humiFog controllers is a low room relative humidity warning. The controller monitors the room humidity probe (or external controller signal) and raises E422 when measured humidity falls below the configured low limit threshold. This is a warning only — humidification continues and the alarm resets automatically when humidity returns above the threshold.

Symptoms

• E422 warning displayed on the controller.
• Room relative humidity reading is below the low limit setpoint.
• Humidifier remains operational; alarm is a signal-only warning.
• Alarm relay closes; automatic reset when humidity recovers.

Common causes

• Actual room humidity is genuinely low — high dry air infiltration or load conditions.
• Humidity probe (room sensor) is faulty, reading lower than actual conditions.
• Low humidity limit threshold set too high relative to actual design conditions.
• Humidifier capacity is undersized for the load, unable to maintain setpoint.
• Humidifier output is restricted by another active fault condition.

Diagnostic steps

1. 01

   Compare room humidity probe reading with a reference instrument

   Use a calibrated handheld hygrometer to measure actual room humidity at the probe location. A large discrepancy indicates probe fault or incorrect installation.

2. 02

   Inspect the humidity probe location and wiring

   Verify the probe is installed in a representative air sample location — not near air inlets, drafts, or localized heat sources — and that wiring connections are secure.

3. 03

   Check the low humidity alarm threshold parameter P3

   Navigate to parameter P3 (low relative humidity alarm threshold) on the type H or T control module and confirm it is set appropriately for the application.

4. 04

   Verify humidifier output is not restricted

   Confirm the humidifier is producing its rated steam output and no other active alarm is limiting production. Check steam pipe routing for blockages or excessive back-pressure.

When to call a professional

If E422 persists despite good probe readings and correct threshold settings, and the room remains consistently below target humidity, the humidifier may be undersized or improperly commissioned for the space. A licensed mechanical engineer or commissioning technician should evaluate system capacity, ductwork distribution, and setpoints.