Carrier furnace code 25: Model Selection or Setup Error
Try DIY first, then call a pro
What does code 25 mean on a Carrier furnace? Official: if code 25 flashes only 4 times at power-up, the model plug PL4 is missing and the control is running on the model stored in memory, and the furnace operates properly. If it flashes continuously: PL4 missing with no valid model in memory (typical after a replacement board), a thermostat call while setup switch SW1-1 or SW1-6 is ON, both switches ON together, or two different furnace models twinned.
Before you touch anything: the six signs that mean stop troubleshooting and call a pro →
GOOD NEWS: THE FIRST CHECKS ARE FREE AND TAKE MINUTES.
Try these first — in this order
Only if you or a tech just had the control door open: confirm SW1-1 and SW1-6 are both OFF. Leave the wiring alone.
Model plug and resistance values get checked against the wiring diagram, and a replacement control has to match the model plug and date code.
What causes it (in order of likelihood)
- Setup switch SW1-1 (code recall) or SW1-6 (component test) left ON DIY-CHECKABLE
- Model plug PL4 missing or wrong after a board replacement (58UVB plugs HK70EZ057 to HK70EZ061 need board date code 4106 or later) TECH
- Two different furnace models twinned TECH
Parts for this code
No specific part number is verified for this code — it typically points at wiring, power, a blown fuse, or communication between components rather than one standard replacement part. If your diagnosis does land on a replaceable component, match its part number against your model's parts list before ordering.
Questions about this code
What does code 25 mean on a Carrier furnace?
Official: if code 25 flashes only 4 times at power-up, the model plug PL4 is missing and the control is running on the model stored in memory, and the furnace operates properly. If it flashes continuously: PL4 missing with no valid model in memory (typical after a replacement board), a thermostat call while setup switch SW1-1 or SW1-6 is ON, both switches ON together, or two different furnace models twinned.
How do I fix Carrier furnace code 25?
If it flashes only four times at power-up, the furnace runs properly. If it flashes continuously, especially after board work, a technician should check the model plug and setup switches.
How much does it cost to fix Carrier furnace code 25?
If it flashes only at power-up, no repair may be needed. Otherwise cost depends on whether setup switches, the model plug, or a mismatched replacement board needs correcting.
Applies to
58MVP (Series 170/180) · 58MVB · 58UVB
Different Carrier generations use different code maps. If your series isn't listed, don't assume this meaning — check your blower-door label.
Verified against Carrier 58MVP/58MVB/58UVB Troubleshooting Guide (58-06T), p.7/19 — “MODEL SELECTION OR SETUP ERROR – Either Indicates the model plug (PL4) is missing or incorrect or setup switch "SW1-1" or "SW1-6" is positioned improperly. If code flashes only 4 times on power-up control is defaulting to model selection stored in memory.”
Verified against Carrier 58MVP/58MVB/58UVB Troubleshooting Guide (58-06T), p.19 — “The model plug is missing or invalid but the control will default to the model stored in memory. The furnace will operate properly as if the model plug was installed.”
Verified against Carrier 58MVB Service and Maintenance Instructions (58MVB-2SM), p.18 — “If status code 25 only flashes 4 times on power-up the control is missing its model plug PL4 and is defaulting to the model selection stored in memory.”
Last verified 2026-09-05 · page updated 2026-10-03 · how we verify
Other Carrier furnace codes
These links include other Carrier model families. Code meanings can change by model and control board, so confirm your model and service manual before using a definition.