York Furnace 3 Green Flashes
StatusShown as: Three green flashes after holding the LAST ERROR button more than five seconds
Confirmation that the stored error code memory has been cleared. Not a fault.
Manual wording: “The LED will flash three green flashes when the memory has been cleared, then will resume the normal slow green flash after a five-second pause.”
Documented for: All UPG boards with a LAST ERROR button
Likely causes, most common first
- The LAST ERROR button was held for more than five seconds, clearing the fault history
When to call a technician
Not a fault. Clearing the fault history erases the evidence a technician uses to diagnose an intermittent problem, so leave the button alone before a service visit.
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 - Two Stage Variable Speed ECM Residential Gas Furnaces, TM9V Series (96% AFUE Multi-position), 1083294-UIM-A-0114 (Johnson Controls Unitary Products (York), TM9V*MP two-stage variable-speed ECM 96% AFUE gas furnaces) · checked 2026-08-25