Trane Furnace Error Code None (Y1 OFF ERR)

The Y1 OFF ERR fault means the furnace control board detected that the Y1 relay output remained OFF when it was commanded ON during a cooling call. Y1 is the first-stage cooling signal that links the thermostat to the air conditioning system through the furnace board. This fault prevents the cooling system from operating. The root cause is typically a failed relay on the control board or an issue in the Y1 wiring circuit.

This fault is not a direct safety hazard in the way that a gas or heat exchanger fault would be. It affects the cooling circuit only and does not impact the furnace heating operation. However, leaving any control board fault undiagnosed for an extended period can allow underlying issues to worsen. Addressing it promptly ensures reliable system operation.

Cycling power to the furnace may temporarily clear the fault code from the display, but if the underlying cause such as a failed relay or wiring fault is still present, the error will return as soon as the system attempts a cooling cycle. A reset alone is not a repair. The Y1 circuit and control board should be properly diagnosed before relying on the system for cooling.

A knowledgeable DIYer can inspect and test the Y1 wiring circuit, check for loose or corroded terminals, and verify 24VAC signal presence at the Y1 terminal during a cooling call. However, if the control board relay has failed, replacing the control board involves working with the furnace electrical system, which many homeowners prefer to leave to a licensed HVAC technician. Always disconnect power to the furnace before inspecting any wiring or components.

If the fix is simply reseating a loose wire or cleaning a corroded terminal, the cost may only involve a service call fee, typically in the range of $75 to $150. If the control board requires replacement, parts and labor combined often range from $400 to $900 depending on the specific board and local labor rates. A thermostat replacement, if that is the source of the faulty Y1 signal, generally runs $100 to $350 installed.