Bryant 355MAV Error Code 42: Inducer Motor Fault
What Does Code 42 Mean?
Status code 42 on the Bryant 355MAV is an inducer motor fault. The inducer, or draft motor, either failed to start within 20 seconds of a call for heat, is running at an RPM outside its valid range, or lost its RPM signal for 5 seconds during operation.
The inducer is the first thing to run in a heating cycle. It pulls a draft through the heat exchanger to vent combustion gases safely outdoors, and its draft is what closes the pressure switches that allow ignition to proceed. If the inducer does not run correctly, the furnace cannot safely ignite, which is why this fault stops the sequence.
A failed inducer motor is the most common cause. Restricted vent pipes or a blocked combustion-air supply can also push the motor outside its normal RPM range by making it work against extra resistance, and improper motor wiring is a less common cause. A homeowner can safely look outside for an obviously blocked vent or intake, but confirming inducer RPM, testing the motor, and checking its wiring are technician tasks on this model.
What You'll Notice
- The furnace does not proceed to ignition; you may hear nothing where the inducer should start
- The inducer may run but sound unusually loud, weak, or uneven
- Grinding, rattling, or screeching noises from the inducer area
- The status LED flashes code 42 (four short flashes, two long flashes)
- No heat is produced because the pressure switches never confirm draft
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| Failed inducer motor | Most common | ✗ Call a pro → |
| Restricted vent or combustion air supply | Common | ✗ Call a pro → |
| Improper inducer motor wiring | Uncommon | ✗ Call a pro → |
How This Is Diagnosed
A technician first checks the exhaust and combustion-air terminations outside and the visible vent piping for blockage, crushing, or sagging that would load the inducer abnormally. The inducer motor is then observed on a call for heat to see whether it starts and holds a valid RPM.
If the venting is clear but the motor will not start, runs out of range, or drops its RPM signal, the motor and its wiring are tested and the motor is typically replaced. Interpreting RPM feedback and replacing the inducer require tools and access to the assembly, so this is professional work.
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:
- The inducer motor does not start at all
- The inducer makes grinding, rattling, or screeching noises
- The outdoor vent and intake are clear but code 42 persists
- The inducer runs but the furnace still will not ignite
- There is a burning smell coming from the inducer motor area
Frequently Asked Questions
What can I safely check myself for code 42?
You can safely look outside for a blocked exhaust or intake pipe — snow, ice, leaves, or a nest — and clear it. Testing the inducer motor's speed and wiring, or replacing the motor, should be done by a technician.
Why won't my furnace ignite with code 42?
The inducer must create proper draft to close the pressure switches before the board allows ignition. With an inducer fault, that draft is not confirmed, so the furnace never lights and stops the cycle for safety.
Sources
✓ Verified against manufacturer service manual — March 2026