Lennox Furnace Error Code E116

E116 indicates that the 24-volt control circuit voltage has exceeded the upper limit of the acceptable range, which Lennox specifies as 18 to 30 volts. The furnace shuts down to protect sensitive control components from damage caused by elevated voltage. The issue is most often linked to high incoming line voltage or a failing step-down transformer inside the unit.

No, continuing to operate the furnace with persistently high control circuit voltage risks damaging the control board, gas valve, and other components connected to the 24V circuit. Repeated exposure to over-voltage conditions can cause failures that are significantly more expensive to repair than addressing the root cause promptly. The furnace should remain off until the voltage issue is identified and corrected.

Repair cost depends on the root cause. If the issue is elevated utility voltage, there may be no parts cost at all, though a service call to diagnose the system typically runs in the range of $75 to $150. Transformer replacement generally costs $150 to $350 including parts and labor. Control board replacement, if that component has been damaged, can range from $300 to $600 or more depending on the board and labor rates in your area.

Some causes, like a utility voltage problem, require contacting your power company rather than replacing any parts. However, diagnosing the exact voltage readings at the transformer and line voltage connections involves working near live electrical components, which carries real safety risk. If you are not experienced with electrical measurements on HVAC equipment, having a licensed technician perform the diagnosis is the safer choice.

Resetting the furnace may temporarily clear the fault and allow the unit to attempt operation again, but if the underlying voltage condition is still present, the E116 code will return quickly. A reset is useful as a first step to confirm the fault is active and repeatable, but it does not correct the electrical issue causing the elevated voltage reading.