Armstrong Air / Aire-Flo · Furnace error code

1 flashFlame sensed with gas valve off

Cross-checked Licensed pro only

Unlock what this code means, its causes, tests and parts

Full library + AI assistant + the OnCall Tech app for iPhone & Android. $34.90, one time.

Stop: this involves gas or the sealed refrigerant system.

OnCall Tech only describes the symptom. Gas work needs a licensed gas technician, and refrigerant work requires EPA Section 608 certification. If you smell gas: shut off the supply if it is safe, do not switch anything on or off, ventilate, leave the building and call the gas utility.

OnCall Tech is a reference tool for trained technicians and can make mistakes. Always disconnect power and confirm with the manufacturer's documentation before you work.

Related diagnostic guides

Guide · Furnace

Igniter glows but burners never light

If the igniter glows and no flame appears, the problem is on the gas side (supply off, valve not opening, valve not receiving 24 V). You can confirm the gas shutoff is open and whether the board sends the valve signal; the valve and gas pressure are licensed-technician work.

3 steps ~30 minadvanced

Guide · Furnace

Bypass humidifier on a furnace: layout, bypass duct, water, drain and 24 V control (install outline)

A bypass humidifier hangs on the supply or return plenum. A short round duct (often 6 in) connects it to the opposite plenum, so the pressure difference across the blower pushes warm air through a wetted water panel and back into the return. A solenoid valve feeds water to the panel only when the humidistat calls and the furnace is heating; unused water runs to a drain or condensate pump. The jobs are: cut and seal two duct openings, run a water line and a drain, wire the 24 V valve through a humidistat and the furnace so it only runs with the blower. Any cut into the furnace cabinet, gas venting or board changes beyond the accessory terminal follow the maker's instructions; many makers state a qualified HVAC contractor should install.

6 steps ~180 minadvanced

Guide · Furnace

Known issue: Trane / American Standard 4YCZ5 gas/electric packaged units, gas valve can open (2025 recall)

In July 2025 Trane Technologies and the CPSC recalled about 4,790 two-stage gas/electric packaged units (models 4YCZ5024F1060A, 4YCZ5036F1070A, 4YCZ5036F1090A, 4YCZ5048E1090A, 4YCZ5048E1115A, specific serial ranges, sold January 2024 to March 2025) because the gas valve could open unexpectedly. Owners were told to stop using heating mode; the installing dealer inspects and replaces the ignition board free. Serial ranges differ slightly between notices, so confirm with Trane.

6 steps ~20 mineasy