Carrier · Furnace

25.4 Main program invalid, running on backup

Low severity 59SC6A

What the control is telling you

The main program is invalid, so the control is using its backup program. Operation is still normal.

Applies to: Carrier 59SC6A

Likely causes

Main program memory corrupted

Test and repair steps

Furnace keeps running; schedule the repair.
Reprogram the control with the rating-plate Model Program Number (app/NFC or super plug).
Verify in the inF menu.
Replace the control if the code returns after reprogramming.

Settings for these units

Filter sizes by casing width and filter cabinet · 59SC6A
Minimum clearances to combustibles · 59SC6A

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Source: Carrier 59SC6A Installation, Start-up, Operating and Service Instructions, Fig. 60 Service Label Information, p.54; Control Board Replacement p.53. 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.