Coleman-Mach LO fault code — Thermostat
Applies to: 9420-381, 9420-382
What LO means
The Coleman-Mach digital thermostat manual says LO displays when current temperature is below 33 F (0 C).
Owner-safe checks
- Compare the thermostat display with room conditions.
- Record whether LO appears continuously or only at startup.
- Avoid changing wiring or internal thermostat settings.
Service-only work
- Sensor faults, thermostat wiring, PTC fuse issues, and HVAC control diagnosis belong to trained technicians.
Safety boundary
Disconnect power before thermostat or HVAC service. Do not probe control wiring unless qualified.