The water heater thermostats are generally used in water heaters as a substitute for Emerson 59T/66T thermostats (manufactured by T.O.D. in the U.S.). This type of electric water heater thermostat combines auto reset and SPST, namely, a single switch controls a single circuit that manipulates a set of normally closed contact points. As temperature rises, the set of normally closed contact points breaks. But as soon as the temperature drops to a specific level for triggering reset, the contact points will reset to be normally closed. The alternative is auto reset + SPDT configuration. Largely identical to the SPST product, it controls one single circuit which manipulates two sets of normally closed contact points. When the contact points reset, auxiliary contact points will break to disconnect from the power supply.