Electronic temperature limiting control

A water heating system comprising:

• a water storage tank;
• one or more heating elements located in the water storage tank and configured to heat water in the water storage tank;
• one or more switches configured to selectively power the one or more heating elements;
• a temperature sensor;
• and
• an energy cutoff apparatus comprising:
• a safety cutoff circuit in electrical communication with the temperature sensor and configured to:
• receive, from the temperature sensor, a temperature signal indicative of whether a water temperature of water in the water heating system is within a permissible water temperature range;
• enable a safe operation current branch responsive at least in part to the temperature signal indicating that the water temperature is inside the permissible water temperature range;
• and
• disable the safe operation current branch responsive to the temperature signal indicating that the water temperature is outside the permissible water temperature range;
• wherein the safety cutoff circuit comprises a plurality of transistors comprising a first transistor configured to receive the temperature signal from the temperature sensor as input;
• and
• a presence detection circuit in electrical communication with the temperature sensor and the safety cutoff circuit, the presence detection circuit being configured to:
• detect whether the temperature sensor is present or absent;
• and
• disable a presence detection current branch responsive to detecting that the temperature sensor is absent,
• wherein the one or more switches are configured to:
• power the one or more heating elements responsive to the safe operation current branch being enabled and the presence detection current branch detecting that the temperature sensor is present;
• and
• disable the heating elements responsive to the safe operation current branch being disabled or the presence detection current branch detecting that the temperature sensor is absent.

A method of energizing heating elements in a water heating system, the method comprising:

• determining, by a presence detection circuit, a whether a temperature sensor is present or absent;
• enabling a presence detection current branch responsive to determining the temperature sensor is present;
• disabling the presence detection current branch responsive to determining the temperature sensor is absent;
• determining, by a safety cutoff circuit, whether a water temperature sensed by the temperature sensor is within a permissible temperature range, wherein the water temperature is detected by the temperature sensor and output by the temperature sensor as a temperature signal, wherein the safety cutoff circuit comprises a plurality of transistors comprising a first transistor configured to receive the temperature signal from the temperature sensor as input;
• and
• enabling a safe operation current branch responsive to the water temperature being within the permissible temperature range;
• and
• disabling the safe operation current branch responsive to the water temperature being outside of the permissible temperature range,
• wherein enablement of the presence detection current branch and the safe operation current branch energizes one or more switches that power the heating elements of the water heating system,
• wherein disablement of the presence detection current branch or the safe operation current branch causes the one or more switches to disable the heating elements of the water heating system.