Rheem R802VA07542117MSA Error Code A126_F: Flame not Sensed with Gas Valve On - UL

What Does Code A126_F Mean?

During a normal ignition sequence, Rheem's Bluetooth Communicating IFC energizes the hot surface igniter, opens the gas valve, then verifies flame presence within seconds through the flame sensor rod. Code A126_F is set when the board has confirmed the gas-valve relay actually closed — voltage applied, valve commanded open — yet the flame sensor still reports no flame. Because that means gas may have been introduced into the burners without being ignited, the IFC treats it as a UL (Underwriters Laboratories) safety alarm and shuts the system down immediately instead of retrying.

A126_F is the inverse of the undesired-flame codes on this two-stage, variable-speed furnace. A126_F means the gas valve is confirmed open with no flame detected — an unburned-gas risk during ignition. By contrast, code A014_F, its one-hour lockout code A116_F, and the UL-flagged code A127_F all describe the opposite mismatch: flame detected while the gas valve should be off. Both directions are safety-critical because both are a disagreement between the commanded valve state and the observed combustion state, but A126_F is specifically the no-flame-with-valve-open case.

Likely causes include a failed igniter that never reaches ignition temperature even though the valve opened on schedule, a flame sensor or its circuit that has failed and can't detect flame even if the burners did briefly light, or a gas valve that opened electrically but isn't delivering adequate gas flow. Any of these leaves the possibility of unburned gas in the furnace, which is why the situation calls for immediate professional attention rather than a homeowner retry. A126_F differs from ordinary failed-ignition codes such as A011_F and A113_F because those are declared when the valve responds normally by closing again after no flame is seen, whereas A126_F is flagged specifically because the valve was confirmed open at the moment the no-flame condition was detected.

What You'll Notice

• The alphanumeric LED blinks out the A126_F fault code digit by digit, with a roughly 3-second pause between digits
• The furnace runs its ignition sequence — igniter glows, inducer runs — but no flame appears and the unit shuts down
• The furnace will not proceed into a heating cycle and will not retry until it is inspected
• A faint gas odor may be noticeable near the furnace during or right after the failed ignition attempt
• No warm air is delivered even though the thermostat is calling for heat

Common Causes

How This Is Diagnosed

With the furnace safely de-energized and the gas isolated, a technician confirms whether the burners actually lit during the sequence, tests the igniter's resistance and glow to see if it reaches ignition temperature, and tests the flame sensor and its circuit independently to rule out a failed sensor masking a real flame. They also verify actual gas flow and pressure at the valve outlet rather than relying solely on the electrical 'valve open' signal.

Because the board confirmed the valve was open when no flame was seen, the technician's priority is establishing whether gas was actually delivered and simply not ignited, versus a sensing failure. That distinction determines whether the igniter, the flame sensor circuit, or the gas valve is at fault, and it is why the furnace is kept off until the check is complete.

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 code appears at all, since a gas-valve-open, no-flame condition risks unburned gas and is unsafe to diagnose without proper tools
• The furnace has attempted to ignite more than once and this code keeps returning
• There is any gas odor near the furnace, even a faint one
• The igniter glows but the burners never light across repeated attempts

✓ Verified against manufacturer service manual — March 2026