Blower motor decided not to shut off during furnace operation-keeps running even after temp set point reached. Thermostat is a digital Hunter, fairly new, been working fine for a few seasons. Would not shut off when set to off at thermostat. Had to turn off at breaker box. Found a pack rat working/building on top of furnace/duct work. Could he have chewed control wires to thermostat causing this problem? How can I test various possible causes?