Low power control system and associated methods for a water heater with flammable vapor sensor

A fuel fired water heating apparatus is disclosed. The water heating apparatus includes: (a) a burner (26) adapted to receive fuel and combustion air and create a flame (60) therefrom, (b) a normally closed fuel valve coupled to the burner for supplying fuel thereto when opened, (c) a thermoelectric circuit (50) which has, connected in series, a thermoelectric device (58) positioned to receive heat from the flame (60) and responsively generate an electrical voltage, a solenoid structure (36) operative to receive electrical power from the thermoelectric device (58) and hold the normally closed fuel valve in an open position and a normally open switch device (61), (d) a low power electrical control circuit (52), which is operable by an electrical power source (72) and coupled to the thermoelectric circuit (50) only via the normally open switch device (61), which is for protecting the heating apparatus against an undesirable operating condition. The low power electrical control circuit (52) has connected therein a variable resistance sensor (46) which is operative to detect the undesirable operating condition. The control circuit (52), in the absence of detection of an undesirable operating condition by the sensor (46), outputs an electrical signal to the switch device (61) to maintain it in a closed state. The switch device (61) terminates the electrical signal upon detection of an undesirable operating condition by the sensor (46) to return the switch device (61) to its normally open state.