Bryant 355MAV Error Code 34: Ignition Proving Failure
What Does Code 34 Mean?
Status code 34 on the Bryant 355MAV indicates an ignition proving failure. The furnace went through its ignition sequence — inducer motor started, igniter heated up, gas valve opened — but the flame sensor did not detect a flame, or the flame was lost shortly after being established.
This is an active fault, not yet a lockout. The control will retry up to three more times before escalating to code 14 (Ignition Lockout), which shuts the furnace down for 3 hours. If flame signal is lost during the blower on-delay period, the blower will come on for the selected blower off-delay.
The most common cause is a dirty or weak flame sensor that has carbon or oxide buildup. The sensor cannot generate enough microamp signal to convince the control board that flame is present. A defective hot surface igniter that does not get hot enough to reliably light the gas is the second most common cause. Low inlet gas pressure or a gas valve that is turned off will also prevent ignition.
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| Dirty or weak flame sensor | Most common | ✗ Call a pro → |
| Defective hot surface igniter | Common | ✗ Call a pro → |
| Low inlet gas pressure or gas valve off | Common | ✗ Call a pro → |
When to Call a Professional
Contact a licensed HVAC technician if:
- Code 34 keeps appearing after cleaning the flame sensor
- The igniter does not glow red-hot during the ignition sequence
- You smell gas but the burners do not light
- The flame lights briefly then goes out within seconds
- The code escalates to lockout code 14 repeatedly
✓ Verified against manufacturer service manual — March 2026