Safety first: Isolate power and allow the booster tank to cool before servicing.

Access booster NTC: Locate the temperature probe on the booster tank. It may be inserted into a dry well or directly into the water.
Check resistance: Disconnect the sensor and measure resistance at ambient temperature. Compare with Meiko’s specification. Replace if open, shorted, or significantly out of range.
Inspect wiring: Trace the cable from the sensor to the control board. Repair any damaged insulation and clean oxidized terminals.
Secure mounting: Ensure the sensor is fully inserted into its pocket or well and has good thermal contact. Poor contact can cause erratic readings.
Control board evaluation: If a new sensor does not resolve E12, the control PCB may not be interpreting the signal correctly and may need replacement by a qualified technician.
Verify rinse temperature: After repair, run several cycles and confirm that final rinse temperature reaches the programmed value.

E12 displayed; booster (final rinse) temperature sensor error, rinse temperature not controlled correctly.

Possible Causes