Goodman Heat Pump Error Code 08

Error code 08 on a Goodman heat pump indicates that the control board has detected line voltage falling outside the acceptable operating window. Specifically, the unit's control circuitry monitors incoming supply voltage continuously, and triggers this fault when voltage drops below 185 VAC or rises above 255 VAC. The standard operating range for a 208/230 VAC single-phase heat pump is roughly 197 to 253 VAC, so the Goodman control provides a slightly wider tolerance band while still protecting compressor and motor windings from damage caused by abnormal voltage conditions.

Low voltage (under 185 VAC) is the more common trigger. It causes excessive current draw in the compressor motor, leading to overheating and premature winding failure. Common sources include a utility supply problem, an undersized or heavily loaded service panel, loose or corroded wiring connections, or an inadequate wire gauge run to the disconnect. High voltage above 255 VAC is less frequent but equally damaging, stressing motor insulation and electronic components. High voltage events are typically caused by utility irregularities, a miswired transformer tap, or a neutral conductor fault.

The control board continuously samples the incoming voltage and will lock out the unit to prevent component damage when the threshold is exceeded. Resetting the fault without resolving the underlying voltage issue will result in the code returning. Diagnosis requires measuring actual supply voltage at the unit disconnect and at the contactor terminals both under no-load and under running conditions, since voltage may sag significantly once the compressor starts.