Carrier 58MVC Error Code 42: Inducer Motor Fault

What Does Code 42 Mean?

The inducer (draft) motor on the 58MVC pulls combustion gases through the heat exchanger and out the vent, and it must reach a valid speed before the burners are allowed to fire. Code 42 is set when the inducer does not start within 20 seconds of a call for heat, when its RPM falls outside the valid operating range, or when the RPM signal is lost for 5 seconds during operation.

On this condensing, sealed-combustion furnace, the inducer draws combustion air through a dedicated intake pipe and exhausts through a second pipe. If the combustion-air supply is restricted — snow, ice, debris, or a nest at the intake termination — the inducer works against too much resistance and its speed reads out of range. Clearing that intake is a homeowner task.

The most common cause overall, however, is a failing inducer motor that cannot reach or hold speed, which the board detects through the motor's speed feedback. Improper motor wiring can also produce or drop the RPM signal. Both of those are internal repairs, not homeowner work.

Unlike the pressure-switch codes (23, 31, 32, 43), which report on draft *proving*, code 42 reports on the inducer motor itself. If the intake and vent are clear but code 42 continues, the inducer motor or its wiring is the likely culprit and a technician should replace or repair it.

What You'll Notice

• The furnace is silent on a call for heat — you never hear the inducer spin up
• The inducer starts but sounds slow, straining, rattling, or unusually loud
• The burners never light because the draft was never proven
• No heat and no other codes that point to airflow or ignition
• The outside intake or exhaust pipe is visibly blocked by snow, ice, or debris

Common Causes

How This Is Diagnosed

The homeowner-checkable step comes first: inspect the outside combustion-air intake and exhaust terminations and clear any snow, ice, leaves, or nests restricting them.

If the terminations are clear and code 42 persists, a technician checks whether the inducer spins freely, tests the motor and its capacitor if fitted, verifies the RPM feedback wiring, and confirms the vent is properly sized. Replacing the inducer motor or repairing its wiring is a professional repair.

How to Fix It: Clear the Combustion-Air Intake and Vent

What You'll Need

• Flashlight
• Gloves

Steps

1. Turn off power at the furnace switch or breaker and shut off the gas supply Set the furnace disconnect to OFF (or trip its breaker) and close the manual gas shutoff valve before inspecting the furnace. If you smell gas, leave the house immediately and call your gas company from outside.
2. Locate the two PVC pipes outside Find where the intake and exhaust pipes terminate at the wall or roof. One draws combustion air in; the other exhausts flue gas. Both must be unobstructed.
3. Clear any blockage Remove snow, ice, leaves, insects, or bird nests from both terminations and the area around them. In winter, keep drifting snow from burying the pipes.
4. Check the pipes are not crushed or disconnected Follow the visible pipe runs for any obvious crushed section or a joint that has pulled apart. Do not attempt internal repairs — just note anything unusual for a technician.
5. Restore power and listen Turn the gas back on, restore power, and call for heat. Listen for the inducer to spin up smoothly within about 20 seconds.

When to Call a Professional

Contact a licensed HVAC technician if:

• The intake and exhaust terminations are clear but code 42 keeps returning
• You never hear the inducer start, or it sounds slow, grinding, or rattling
• A visible vent pipe section is crushed, disconnected, or damaged
• You are not comfortable inspecting the furnace or its venting

✓ Verified against manufacturer service manual — March 2026