Carrier Furnace Code 34
WarningShown as: 3 short flashes, 4 long flashes
Ignition proving failure. Flame was not sensed during the trial for ignition. The control will retry three more times before going to ignition lockout (code 14).
Manual wording: “34 IGNITION PROVING FAILURE - Control will try three more times before lockout #14 occurs.”
Documented for: 58SC0A, 58MCB, 58MVP, 58UVB
Likely causes, most common first
- Low inlet gas pressure
- Gas valve defective or turned off / manual shut-off valve closed
- Defective hot surface igniter
- Oxide buildup on the flame sensor
- Loss of control ground continuity - the green/yellow wire must be connected to the furnace sheet metal
- Flame sensor grounded or misplaced
- Inadequate flame carryover or rough ignition
What you can safely check yourself
- Confirm other gas appliances in the house still work so you know gas service is on
- Check that the furnace door is fully closed
When to call a technician
Cleaning the flame sensor, checking microamp flame current, and testing the igniter all require opening the burner compartment on a live gas appliance. Call a technician.
A Carrier furnace throwing this code repeatedly has a reason — clearing the code without fixing the cause just hides it.
Sources
- 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
- Installation, Start-Up, Operating and Service and Maintenance Instructions - 58SC0A/58SC1A (Carrier, 58SC0A/58SC1A single-stage 4-way multipoise condensing gas furnace) · checked 2026-08-25
- 58MCB 4-Way Multipoise Fixed-Capacity Condensing Gas Furnace - Service Manual (Carrier, 58MCB single-stage condensing gas furnace) · checked 2026-08-25