I went on a call last week, new construction, ICF house, Dual fuel heat pump. Home owner acting as own contractor. One of the systems had blank stat and wouldn't work, I thought of the pack rats that had chewed up low voltage wires after install. No power at furnace, breaker was good had power, rechecked outlet, had power. The homeowner had installed tamper resistant recept. and the plastic covers were not allowing contact to furnace plug, took 15 minutes to diagnose and replace with standard recept. He argued for longer, about me charging him.