Arrived to diagnose a furnace that reaches the overheat limit very quickly. Tested system airflow and verified that the system is moving air properly. Verified that the system is actually getting too hot. Continued extensive diagnostic with special tools brought out from the warehouse. Determined the gas valve is not operating properly. Also, found that the inducer is leaking flue condensation. Spoke with homeowner about repair solutions. Homeowner declined repairs at this time.