Carrier 58MVC Error Code 25: Model Selection or Setup Error

What Does Code 25 Mean?

The 58MVC's variable-speed control has to know exactly which furnace model and configuration it is running, because that determines airflow tables, gas staging, and operating limits. It reads that identity from a model plug (PL4) and a bank of setup switches. Code 25 is a configuration fault: either the model plug is missing or incorrect, or setup switch SW1-1 or SW1-6 is positioned improperly.

If the code flashes only four times on power-up, the control is defaulting to a model selection stored in memory. If it flashes continuously, the board is not reading a valid model plug at all. The manual notes several specific conditions to check: a thermostat call with SW1-1 on, a thermostat call with SW1-6 on, both SW1-1 and SW1-6 on together, and two different furnace models twinned. It also notes that newer model plugs (HK70EZ017-021) are only recognized by board software version V12 or later, so an older board paired with a new plug can trigger this code.

Because this code is about configuration rather than a failed part, its severity is lower than the lockout codes — the furnace is not necessarily damaged. But running it on the wrong configuration can cause improper airflow or staging, so the setup must be corrected.

Verifying the model plug, reading resistance values against the wiring diagram, and setting DIP switches are service tasks tied to the specific installation, and they are best handled by a technician who can confirm the correct settings for your furnace.

What You'll Notice

• The status LED flashes code 25 (either four flashes on power-up, or continuously)
• The code appears right after a control board replacement or other service work
• The furnace may run improperly, stage oddly, or move the wrong airflow
• In twinned or newly configured systems, the setup does not behave as expected
• A newly installed model plug is not recognized by an older board

Common Causes

How This Is Diagnosed

A technician checks whether the code flashes four times (defaulting to stored memory) or continuously (no valid plug read), which narrows the cause. They confirm the correct model plug (PL4) is installed and reads the right resistance against the wiring diagram, and they verify the setup switches SW1-1 and SW1-6 are in the correct positions for the installation.

They also confirm board software compatibility if a newer model plug is used, since plugs HK70EZ017-021 require software version V12 or later. Setting the configuration correctly for the specific furnace is a service task best left to a professional.

When to Call a Professional

This code involves components that are not homeowner-serviceable, so have a licensed HVAC technician diagnose and repair it. Keep in mind:

• Contact a technician to verify the model plug and setup switch configuration for your specific furnace
• If the code appeared right after a board replacement, have the installer confirm the correct model plug and DIP switch settings
• If a new model plug is not recognized, the board may need a software version that supports it
• Do not guess at DIP switch positions — incorrect settings can cause improper airflow or gas staging

✓ Verified against manufacturer service manual — March 2026