SEN
Laars
Temperature Sensor Failure or Out-of-Range Reading
Boiler displays SEN or Sensor Error; may indicate supply, return, or flue sensor fault.
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Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
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Possible Causes
Open or shorted NTC temperature sensor, Damaged sensor wiring harness, Sensor not properly inserted in well, Control board reading error
How to Fix / Troubleshooting
Safety first: Turn off power before accessing sensors or wiring. Surfaces may be hot; allow to cool.
- Identify which sensor: The Laars control may specify SPLY, RET, or FLUE along with SEN. Note which one is indicated.
- Inspect wiring: Trace the sensor cable from the sensor to the control board. Look for cuts, abrasions, or loose connectors. Reseat the plug at the control.
- Check sensor placement: Ensure the sensor is fully inserted into its well or strapped tightly to the pipe as designed.
- Compare temperatures: If you have an infrared thermometer, compare the actual pipe temperature to the displayed value. A large discrepancy suggests a bad sensor.
When to call a professional: Sensor resistance testing and replacement, and control board diagnosis, should be handled by a technician.
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Repair Difficulty
Medium
3/5
Required Part
NTC Temperature Sensor
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