Bryant 315AAV Error Code 34: Ignition Proving Failure
What Does Code 34 Mean?
An ignition proving failure (status code 34) on the Bryant 315AAV means the igniter heated and the gas valve opened, but the flame-sensing rod could not confirm a stable, adequate flame. Rather than lock out immediately, the control tries three more times; if it still cannot prove flame, the condition escalates to status code 14, the ignition lockout.
The flame sensor works by rectifying a tiny current through the flame — Bryant specifies roughly 4 to 6 microamps DC, about 5 nominal. When oxide builds up on the sensor rod, that signal drops and the control reads it as 'no flame' even though the burners lit. That is why Bryant lists oxide buildup on the flame sensor as the leading item to check, along with proper microamps, a manual valve that is shut off, low inlet gas pressure (where a low gas pressure switch is used), a defective or turned-off gas valve, and a flame sensor that must not be grounded.
While flame-sensor service is what most often resolves this, the mix of flame-sense and gas-side causes on this code means it is diagnosed and repaired by a technician, who can measure the microamp signal and check gas pressure safely.
What You'll Notice
- The burners light but then drop out, and the furnace tries again a few seconds later
- You may see the igniter glow and a brief flame that does not stay established
- The status LED flashes three short then four long flashes
- If the retries fail, the furnace escalates to code 14 and stops trying for about 3 hours
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 → |
How This Is Diagnosed
A technician confirms the burners actually light, then measures the flame-sensor signal against the specified 4 to 6 microamps DC; a low or unstable reading points to a fouled or failing sensor rod, which is cleaned to bare metal or replaced. They also confirm the manual gas valve is open and inlet pressure is adequate, verify the gas valve is functioning, and check that the flame sensor is not grounded. The flame-sense side is checked first because it is the most common cause.
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 burners light briefly and then drop out repeatedly
- The furnace keeps escalating from code 34 to a code 14 lockout
- You have confirmed the gas is on to the house, yet flame will not stay proven
- Any flame-sensor service or gas-pressure check, which requires a technician's meters
Frequently Asked Questions
What is the difference between code 34 and code 14?
Code 34 is the ignition proving failure while the control is still retrying. Code 14 is the lockout that follows once the retries are exhausted, when the furnace stops trying for about 3 hours.
Why does the furnace light and then shut right off?
The burners are lighting, but the flame sensor cannot confirm a strong enough flame signal — most often because oxide has built up on the sensor rod — so the control drops the flame and retries.
Can I clean the flame sensor myself?
Because code 34 also involves gas-side causes and requires measuring the flame-sensor microamps, this furnace's ignition proving fault is best handled by a technician who can verify the signal and gas pressure safely.
Sources
✓ Verified against manufacturer service manual — March 2026