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Carrier · Furnace

45 Control circuitry lockout

High severity 59TP6A58SB0A/58SB1A

What the control is telling you

Control locks out (auto-reset after 1 hour) due to a flame circuit failure, stuck-open gas valve relay or software check error.

Applies to: 59TP6A two-stage variable-speed ECM multipoise condensing gas furnace, all sizes (040-10 to 120-22)

Likely causes

  • Flame circuit failure on control
  • Gas valve relay stuck open
  • Software check error

Test and repair steps

  1. Warning: Shut off 115-V power and gas, and lock/tag out before working inside the furnace; there may be more than one power source.
  2. Reset power to clear the lockout.
  3. Run a heat cycle and watch for the code to return.
  4. If code 45 repeats, replace the furnace control (install model plug PL4 on the new board).

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Source: Carrier 59TP6A Installation, Start-up, Operating and Service Instructions, Fig. 66 Troubleshooting Guide (cont.), p.89. Summarized in our own words; check the original manual for your model.

Homeowner looking at this code? See what it means for you and when to call a technician.

For licensed technicians. Gas, electrical and refrigerant work must be done by a qualified, licensed person. Shut off power and gas before servicing, never bypass a safety control, and follow the manufacturer’s manual for the exact model; it and local codes always take priority. HVACopedia is not affiliated with any manufacturer; brand and model names only identify the equipment.