making it compatible with standard HVAC control circuits

leading to "arching" where the spark jumps to the chassis instead of reaching the electrode

preventing hunting and ensuring the thermal expansion valve maintains the exact mass flow required by the evaporator

always match the original RPM specs

and drip shields required to manage condensate and maintain thermal integrity when the airflow direction is reversed

Lochinvar & A.O. Smith 100108421 Lower Thermostat 30067439-890 making it compatible with standardFor professional contractors servicing Lochinvar or A. O. Smith residential electric units, the 100108421 Lower Thermostat is the critical OEM replacement part required to maintain precise thermal regulation. This WH9 lower thermostat is the officially authorized update for the legacy 9000507005 and 9000507015 models. Engineered with a patented bimetal sensor, this component ensures maximum temperature sensitivity and responsiveness to tank