I completed a diagnostic on a heat pump. The homeowner advised that the day before the thermostat gave an alert 126.00 Comm error. I started the heat pump and ran it through tests. Outdoor fan worked properly and drive board operated. Voltages were correct. I found low voltage comm wires outside had been chewed on by rodent. I repaired wires and restored power. The error went away and system is operating properly at this time.
