it will not generate the vacuum needed to close the pressure switch

though a failing internal relay in the control board can also be the culprit

The Reznor 209339 Spark Electrode (also identified as PSE-RZ9) is the direct OEM replacement engineered to deliver consistent high-voltage arcing to ignite the gas-air mixture across various unit heater and air handler platforms

Common Questions When is an isolation relay kit required for a heat pump

Lochinvar & A.O. Smith 100271315 Limit Switch 30067439-890 it will not generate theThe Lochinvar & A. O. Smith 100271315 Limit Switch is a critical safety component engineered for high performance hydronic and water heating systems. As a veteran technician knows, maintaining the integrity of the safety loop is non negotiable. This OEM high limit switch is designed to monitor outlet water temperature and provide a positive safety shutdown by interrupting the electrical circuit if temperatures exceed the factory set threshold,