Bryant 315AAV Error Code 34: Ignition Proving Failure
What Does Code 34 Mean?
Status code 34 on the Bryant 315AAV indicates an ignition proving failure. The furnace either failed to detect a flame after the gas valve opened, or the flame was detected but then lost during operation. The control will try three more times before escalating to lockout code 14. If the flame signal is lost during the blower on-delay period, the blower will come on for the selected blower off-delay to clear any unburned gas from the combustion chamber.
The flame sensor is a thin metal rod positioned in the burner flame path. It works by detecting a small electrical current (microamps) that flows through the flame. The manufacturer specifies a minimum of 5 microamps DC, with 4.0 to 6.0 microamps being the normal operating range. When the sensor rod becomes coated with oxide buildup, this current drops below the threshold, and the control board interprets it as no flame present.
The most common cause is oxide buildup on the flame sensor rod. Other causes include a closed manual gas shutoff valve, low inlet gas pressure, a defective gas valve, or a flame sensor that has become grounded. Checking the gas supply valve is a quick first step before cleaning the sensor.
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| Dirty flame sensor (oxide buildup) | Most common | ✗ Call a pro → |
| Low gas pressure or manual valve shut-off | Common | ✗ Call a pro → |
| Defective gas valve | Uncommon | ✗ Call a pro → |
When to Call a Professional
Contact a licensed HVAC technician if:
- The burners still fail to stay lit after cleaning the flame sensor
- The hot surface igniter does not glow during the ignition sequence
- You can hear gas flowing but it does not ignite
- The flame appears yellow, lazy, or rolls out of the combustion chamber
- Code 34 occurs repeatedly even with a clean flame sensor
✓ Verified against manufacturer service manual — March 2026