Durable Construction: Heavy-duty copper capillary resists corrosion and fatigue in high-heat zones

If the furnace blower runs continuously while the burners remain off

Reference the LED diagnostic light on the board surface

or CE60 wall box

Lochinvar & A.O. Smith 100109151 Switch 319852-301 Durable Construction: Heavy-duty copper capillaryThe Lochinvar & A. O. Smith 100109151 is a critical safety component designed for high efficiency BTH (Best Tankless Hybrid) water heaters and commercial boilers. This Low Gas Pressure Switch is factory calibrated to a 5" WC (Water Column) set point, serving as a primary sentry to ensure safe combustion cycles. In the field, this switch monitors the incoming gas supply pressure to prevent the burner from firing under insufficient pressure conditions,