Carrier Furnace Code 42
WarningShown as: 4 short flashes, 2 long flashes
Inducer motor fault. The inducer did not start within 20 seconds of a call for heat, its RPM is outside the valid range, or the RPM signal was lost for 5 seconds during operation.
Manual wording: “42 INDUCER MOTOR FAULT - Indicates the inducer has not started within 20 seconds after a call for heat, the inducer motor RPM is outside its valid range of operation, or the inducer RPM signal was lost for 5 seconds during operation.”
Documented for: 58MVP, 58UVB and other variable-speed two-stage Carrier furnaces
Likely causes, most common first
- Improper vent sizing
- Restricted combustion air supply
- Failed inducer motor
- Improper motor wiring
What you can safely check yourself
- Check the outdoor intake and exhaust pipes for snow, ice, or debris blocking them
When to call a technician
The inducer motor and its wiring have to be tested by a technician. A furnace that cannot run its inducer cannot vent combustion gases safely.
A Carrier furnace throwing this code repeatedly has a reason — clearing the code without fixing the cause just hides it.
Source
- Troubleshooting Guide - Variable Speed, Two-Stage Gas Furnaces (Form 58-06T) (Carrier, 58MVP, 58UVB and other Carrier variable-speed two-stage gas furnaces (replaces 58MVP-10SM)) · checked 2026-08-25