Rheem R802VA07542117MSA Error Code A126_F: Flame not Sensed with Gas Valve On - UL
What Does Code A126_F Mean?
Fault code A126_F on the Rheem R802VA is a UL (Underwriters Laboratories) safety fault that occurs when the IFC has confirmed the gas valve is energized and open, but the flame sensor is not detecting any flame. This is a critical safety condition because it means gas may be flowing into the furnace without being ignited.
During a normal ignition sequence, the IFC energizes the hot surface igniter, opens the gas valve, and then verifies flame presence within a few seconds via the flame sensor. If the valve is confirmed open (the relay has closed and voltage is applied) but flame is not detected, A126_F is set as a UL-level alarm. The UL designation means this fault is tied to the furnace's safety listing requirements.
Possible causes include a failed igniter that cannot heat to ignition temperature even though the gas valve has opened, a flame sensor that has completely failed and cannot detect flame even when the burners light momentarily, or a gas valve that is providing inadequate gas flow despite being electrically commanded open. In any of these cases, the risk of unburned gas in the furnace is present and the situation requires immediate professional attention.
Common Causes
When to Call a Professional
Contact a licensed HVAC technician if:
- Do not attempt to restart the furnace — call a technician immediately
- A technician must verify whether the burners are actually lighting or whether gas is flowing without ignition before any restart is attempted
- The igniter, flame sensor, and gas valve all need professional testing to identify the root cause of this UL safety fault
✓ Verified against manufacturer service manual — March 2026