Lennox Heat Pump Error Code OFF/OFF

OFF/OFF indicates that the control board is receiving no 24-volt power at its R and C terminals, so its diagnostic LEDs are completely dark. This points to a problem in the low-voltage power supply circuit, such as a failed control transformer, a blown fuse, or an open wire. If 24V is confirmed at the board terminals and the LEDs still do not light, the board itself has failed and needs replacement.

No. An OFF/OFF condition means the control board has no power and the system is completely non-operational. Attempting to force the system to run is not possible in this state, and the underlying cause, such as a short circuit or failed transformer, should be resolved before restoring power to prevent further component damage.

Repair costs vary depending on the failed component. Replacing a blown low-voltage fuse is inexpensive, typically in the range of a service call fee. A new control transformer generally runs between $50 and $150 in parts, while a replacement control board can cost anywhere from $150 to $400 or more depending on the model. Add labor charges to these estimates for a full cost picture.

Some steps, like checking for a tripped breaker or inspecting visible wiring connections, are within reach of a careful DIYer. However, measuring transformer output voltage, testing fuses, and replacing control boards or transformers involves working near line-voltage components and requires proper safety precautions. If you are not comfortable with electrical diagnostics, a licensed HVAC technician should handle the repair.

A simple reset will not resolve OFF/OFF because the condition reflects a true loss of 24V power to the board rather than a stored fault code. The root cause, whether a failed transformer, blown fuse, open wiring, or failed board, must be diagnosed and corrected before the system can power up and operate normally.