Lennox Air Conditioner Error Code E426

E426 means the inverter control has locked out the system after recording ten inverter fault events within one hour. This is a protective lockout, not a single isolated failure. The code indicates that an underlying system condition such as incorrect refrigerant charge, a failed fan motor, or a restricted TXV has been causing repeated inverter alarms until the threshold was reached.

A power reset will clear the active lockout and allow the system to restart, but it will not fix whatever is driving the repeated inverter alarms. If the root cause such as low refrigerant, a failed condenser fan, or a restricted TXV is not repaired, the system will reach ten faults again within an hour and lock out again. A permanent resolution requires diagnosing and correcting the underlying system problem.

Repair costs vary widely depending on the root cause. A refrigerant charge correction typically runs in the range of $150 to $400 depending on the amount of refrigerant involved and whether a leak repair is needed. Component replacements such as a condenser fan motor or TXV can range from $300 to $800 or more including labor. A diagnostic visit from a certified HVAC technician is generally required first to identify which component or condition is responsible.

You can attempt a reset by disconnecting power to the outdoor unit and then restoring it, which is the first recommended step. However, if the underlying cause is not corrected, the unit will accumulate ten faults again and lock out a second time. Before resetting, review the alarm history on the control board so you understand which specific fault has been repeating.

The E426 lockout prevents the system from running, which is itself a protective state. You should not attempt to repeatedly reset and restart the unit without diagnosing the cause, as doing so can accelerate wear on the compressor and inverter drive components. Have a qualified technician review the alarm history and perform a full system inspection before returning the unit to regular operation.