York Furnace 1 Red Flash
Safety faultShown as: One red flash, then a two-second pause, repeating
Flame was sensed when there was no call for heat. The control saw a burner flame while the gas valve should have been closed, so it runs the inducer and the blower to clear the heat exchanger.
Manual wording: “1 RED FLASH: This indicates that flame was sensed when there was not a call for heat. The control will turn on both the inducer motor and supply air blower. Check for a leaking or slow-closing gas valve.”
Documented for: TG8S, TG9S, TM9E, TM9X, TM8X, TM9T, TM8T, TM8Y, TM9Y
Likely causes, most common first
- Leaking gas valve
- Slow-closing gas valve
What you can safely check yourself
- If you smell gas, leave the house and call the gas utility from outside
When to call a technician
This means gas may be reaching the burners when it should not. Call a licensed technician right away - the gas valve has to be tested and replaced by a professional.
A York furnace throwing this code repeatedly has a reason — clearing the code without fixing the cause just hides it.
Sources
- Installation Manual - Single Stage PSC Residential Gas Furnaces, TG9S and GG9S Series (95.5% AFUE Multi-position), 1083287-UIM-A-0114 (Johnson Controls Unitary Products (York), TG9S*MP, GG9S*MP single-stage PSC 95.5% AFUE gas furnaces) · checked 2026-08-25
- Installation Manual - Single Stage PSC Residential Gas Furnaces, TG8S*MP / TGLS*MP / GG8S*MP / GGLS*MP (80% AFUE Multi-position / Standard Low NOx), 998491-UIM-B-1013 (Johnson Controls Unitary Products (York), TG8S*MP, TGLS*MP, GG8S*MP, GGLS*MP 80% AFUE single-stage gas furnaces) · checked 2026-08-25
- Installation Manual - Single Stage ECM Residential Gas Furnaces, TM9E Series (95% AFUE Multi-position), 1083163-UIM-A-0214 (Johnson Controls Unitary Products (York), TM9E*MP single-stage ECM 95% AFUE gas furnaces) · checked 2026-08-25