Lennox Furnace Error Code E280

E280 indicates that the furnace detected no 24-volt output on the Y1 terminal to the common terminal when attempting to communicate with a non-communicating outdoor unit. The Y1 relay, also called the Stage 1 relay, either did not energize or its contacts failed to close. This prevents the furnace from sending a compressor call signal to the outdoor unit. The fault is rooted in the Y1 pilot relay circuit on the control board.

A reset may temporarily clear the E280 code, but if the underlying relay or control board fault still exists, the code will return as soon as the system attempts another Y1 call. Resetting is a useful first step to confirm whether the fault is intermittent or persistent, but it does not repair a failed relay or a wiring problem. Persistent E280 faults require component-level diagnosis and repair.

Repair costs depend on the root cause. If the fix involves correcting a wiring connection, the cost may be limited to a service call fee, typically in the range of $75 to $150. If the control board requires replacement, parts and labor combined can range from $400 to $900 or more depending on the specific board and local labor rates. A technician diagnosis is needed to confirm which component is at fault before estimating the total repair cost.

Diagnosing E280 requires measuring 24 VAC at specific terminals and inspecting the control board relay, which involves working inside an energized furnace panel. Homeowners comfortable with basic electrical testing can start by checking the low-voltage wiring between the furnace and outdoor unit for loose connections or damage. However, if the control board relay or the board itself has failed, replacement is best handled by a qualified HVAC technician to ensure correct installation and safe operation.

The furnace heating function may still operate with E280 active, since this fault specifically affects the Y1 cooling or heat pump call circuit. However, running the system without addressing the fault means your outdoor unit will not respond to cooling or heat pump calls, which can cause comfort issues and may lead to additional fault codes. It is advisable to have the fault diagnosed promptly to prevent further stress on control board components.