HVACopedia

Carrier · Furnace

21 Gas heating lockout

Critical severity 59TP6A58SB0A/58SB1A

What the control is telling you

The control locked out of gas heating; it points to the gas valve relay or gas valve wiring.

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

Likely causes

  • Gas valve relay on control stuck closed
  • Miswire or short on the gas valve wire

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. Turn off power, wait 5 minutes and retry.
  3. Inspect gas valve wiring for miswiring or a short.
  4. If the fault returns with wiring correct, the control's gas valve relay is stuck closed; replace the furnace control.

Settings for these units

Save it for the next call

Star this code in the HVACopedia app and keep the whole library on your phone for jobs with no signal.

Open the app

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.