Fluid-heating apparatus, circuit for heating a fluid, and method of operating the same

A fluid-heating apparatus for heating a fluid, the fluid-heating apparatus being connectable to a power source, the fluid-heating apparatus comprising:

• a vessel;
• an inlet to introduce the fluid into the vessel;
• an outlet to remove the fluid from the vessel;
• a heating element at least partially surrounded by the fluid in the vessel, the heating element comprising a wire, an insulating material surrounding at least a portion of the wire, and a sheath surrounding at least a portion of the insulating material;
• a ground contact in electrical communication with the sheath;
• a control circuit connectable to the power source and connected to the heating element, the control circuit comprising a current path having a first leg connecting the power source to a first point of the heating element and a second leg connecting the power source to a second point of the heating element, a switch connected in circuit in the first leg, and a current sensor connected to the current path, the control circuit being configured to
• initiate a heating state of the fluid-heating apparatus by establishing a current in the current path, the establishing act comprising making the switch to allow current in the first current path,
• initiate a non-heating state and ceasing the heating state of the fluid-heating apparatus by ceasing the current in the current path, the ceasing act comprising breaking the switch to not allow current in the first current path,
• allow connection of the power source to the second point of the heating element during the non-heating state thereby allowing a current in the second leg during the non-heating state,
• sense a leakage current of the heating element during the connection of the power source to the second point of the heating element during the non-heating state;
• and
• determine a degradation of the heating element prior to a failure of the heating element with the sensed leakage current.

A fluid-heating apparatus for heating a fluid, the fluid-heating apparatus being electrically connectable to a power source, the fluid-heating apparatus comprising:

• a vessel;
• an inlet to introduce the fluid into the vessel;
• an outlet to remove the fluid from the vessel;
• a heating element at least partially surrounded by the fluid in the vessel, the heating element comprising a wire, an insulating material surrounding at least a portion of the wire, and a sheath surrounding at least a portion of the insulating material;
• a ground contact in electrical communication with the sheath;
• a control circuit connectable to the power source and connected to the heating element, the control circuit comprising a first current path having a first leg connecting the power source to a first point of the heating element and a second leg connecting the power source to a second point of the heating element, a switch connected in circuit in the first leg, a second current path connecting a low-voltage power supply to the heating element via the switch, and a current sensor connected to the second current path, the control circuit being configured to
• initiate a heating state of the fluid-heating apparatus by establishing a current in the first current path, the establishing act comprising making the switch to allow current in the first current path,
• initiate a non-heating state and ceasing the heating state of the fluid-heating apparatus by ceasing the current in the current path,
• connect the low-voltage power supply to the heating element during the non-heating state thereby allowing a current in the second current path during the non-heating state,
• sense a leakage current of the heating element during the connection of the low-voltage power supply to the heating element;
• and
• determine a degradation of the heating element prior to a failure of the heating element with the sensed leakage current.