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Carrier · Furnace

25 Invalid model selection or setup error

Medium severity 59TP6A

What the control is telling you

If 25 flashes only 4 times at power-up, model plug PL4 is missing and the control is using the model stored in memory. Flashing continuously indicates a setup error.

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

Likely causes

  • Model plug PL4 missing and no valid model stored (common on replacement controls)
  • Thermostat call with SW1-1 ON
  • Thermostat call with SW1-6 ON
  • SW1-1 and SW1-6 both ON
  • Two different furnace models twinned
  • Wrong replacement control (needs non-modulating board, software V17 or later)

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. Check that model plug PL4 is installed on the control, especially after a control replacement.
  3. Set SW1-1 and SW1-6 OFF for normal operation.
  4. If twinned, confirm both furnaces are the same model.
  5. On a replacement control, verify it is the non-modulating board with software V17 or later.
  6. Restore power and confirm the code clears.

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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.

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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.