E18
Monarch Brine Concentration / Conductivity Sensor Error

E18 error and the unit indicates a brine concentration or conductivity fault (on models with brine sensor)

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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

Insufficient salt in brine tank, Sensor coated with sludge, Sensor wiring fault, Failed brine conductivity probe

How to Fix / Troubleshooting

Safety first: Turn off power before handling sensors in the brine tank.

  • Check salt quantity: Ensure the brine tank is at least half full of the correct Monarch-approved salt type.
  • Stir brine: If the unit has not regenerated for a long time, the brine may be stratified. Use a plastic stick to gently stir the water around the sensor.
  • Clean sensor: Remove the brine sensor if accessible and rinse it in warm water. Gently remove any sludge or deposits.
  • Inspect cable: Check the sensor cable for damage and ensure it is firmly connected to the PCB.
  • Test after regeneration: Run a manual regeneration and see if E18 clears once fresh brine is made. Persistent errors may require sensor replacement.
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Repair Difficulty

Medium 3/5

Required Part

Brine Conductivity Sensor
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