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51

Error 51 — Refrigerant pressure sensor failure

Lennox · EL18KSLV Series Outdoor Units

What does 51 mean?

There is an electrical failure with the sensor that measures the system's refrigerant pressure. This sensor is connected to the PCB.

Common Causes

  • Sensor short circuit
  • Sensor open circuit
  • Loose sensor connection
  • Defective sensor

Repair Steps & Checklist

Click steps to track your progress.

  1. 1

    Check the connection of the refrigerant pressure sensor to the PCB.

  2. 2

    Inspect the sensor wiring for damage.

  3. 3

    Replace the sensor if it is faulty.

Browse all codes in this manual (43)
Verified technical data. Last updated: April 2026

Related Faults

1Error 1 — EEPROM malfunction or damage10Error 10 — Outdoor defrost sensor failure11Error 11 — Suction temperature sensor failure
Source: Lennox EL18KSLV Series Outdoor Units
Open Manual (Page 68)Search more codes in this manual