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Irritrol RD-900 Randomly Stops, Displays Flashing "SEN" Code

A 6-month-old RD-900 randomly halts watering and flashes "SEN" alternating with the time. Opening/closing the programming module sometimes resets it. The system works for days or weeks between episodes.

What "SEN" Means

SEN = Rain/Moisture Sensor Active. The controller has a rain sensor connected, and when moisture is detected, it suspends watering for the programmed number of "rain delay" days.

Immediate Bypass Solution

On the back of the controller (top right), there's a slide switch labeled ACTIVE / BYPASS. Move it to BYPASS to disable the sensor input immediately. The system will resume normal operation.

Long-Term Fixes

Adjust sensor sensitivity - Most sensors have a vent ring or adjustment cap to change drying time
Relocate sensor - Move it to a sunnier, better-ventilated location
Replace sensor - If it's oversensitive or faulty
Check rain delay setting - Reduce the number of days the controller waits after rain

Download the Manual

Visit irritrol.com for the complete RD-900 manual covering programming, sensor setup, and troubleshooting.

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