Lennox Mini Split P3 Error Code

What P3 means

P3 on Lennox mini splits means outdoor unit low-temperature lockout: in heating, the outdoor unit locks out when the temperature stays below -13 F (-25 C) for one hour (MPA/MPB units; MLA units lock out at -22 F). This is protective, not broken - the unit resumes when it warms above about -7.6 F (-22 C) or 23 F. If P3 appears in mild weather, the outdoor ambient sensor or control is misreading and needs service.

First checks before service

This page currently documents the safe reset triage. If the code returns, use the linked source manual or a qualified technician for code-specific diagnosis.

1. 1. One-time fault event (power disturbance or transient sensor reading) common DIY

   Check: Power-cycle at the breaker/disconnect (or unplug for CPAP), restore, and run the system while watching for the code.

   Fix: If the code does not return after a full run cycle, the fault was transient — monitor, no repair needed.

2. 2. Fault persists after a clean reset occasional pro only

   Check: If the code returns immediately or every session, note the conditions (startup, heating, after rain).

   Fix: A persisting code points at the component the manual assigns to this code — that repair is technician territory.