In an electric water heater having adjustable set point and differential temperatures, upper and lower heating elements, and associated temperature sensors respectively operative to sense upper and lower tank water temperatures, a specially designed control system is provided for controlling the heating elements. The control system is operative to prevent dry firing of the heating elements by measuring temperatures over time with the temperature sensors.

A hot water tank including: a shell enclosing a chamber containing a heat exchange liquid, the shell including a base, side wall and lid; a cold water inlet connected to a first end of a heat exchanger, and a hot water outlet connected to a second end of the heat exchanger, wherein the heat exchanger is located in an upper portion of the chamber; a primary heating element connected to a power source for heating the heat exchange liquid, the primary heating element being located in a lower portion of the chamber.

A glue rewarming device includes a glue pipe, a main body, a plurality of temperature sensors, a timer, and a control terminal. Each glue pipe is configured to receive glue. The main body defines the grooves spaced apart from each other. Each groove is configured to receive one glue pipe. Each temperature sensor is in one groove and on an inner wall of the one groove. The temperature sensor is configured to sense a temperature of the glue in the glue pipe inserted into the corresponding groove. The timer is configured to record a time point when the glue pipe is placed in one groove and a time length from the time point when the glue pipe is placed in one groove to the time when the glue in the glue pipe reaches a target temperature. The control terminal is electrically connected to the timer and the temperature sensors.

A glue rewarming device includes a glue pipe, a main body, a plurality of temperature sensors, a timer, and a control terminal. Each glue pipe is configured to receive glue. The main body defines the grooves spaced apart from each other. Each groove is configured to receive one glue pipe. Each temperature sensor is in one groove and on an inner wall of the one groove. The temperature sensor is configured to sense a temperature of the glue in the glue pipe inserted into the corresponding groove. The timer is configured to record a time point when the glue pipe is placed in one groove and a time length from the time point when the glue pipe is placed in one groove to the time when the glue in the glue pipe reaches a target temperature. The control terminal is electrically connected to the timer and the temperature sensors.

A combination boiler provides heated water to a boiler loop and domestic hot water (DHW) to a domestic water loop. The combination boiler includes a primary heat exchanger (PHE) connected to the boiler loop and a burner to provide heat to the primary heat exchanger. A secondary heat exchanger (SHE) transfers heat energy from the boiler loop to the domestic water loop. A controller monitors a PHE inlet temperature and a DHW output temperature, obtains a pre-heat initialization temperature threshold and a pre-heat cancellation temperature threshold, and detects a low temperature condition. A pre-heat operation is initiated responsive to the low temperature condition by circulating heated water from the PHE to the SHE. The burner is selectively fired at least in part according to an outlet temperature of the PHE.

A water heating system can include a first tank-based water heater having a first inlet line and a first outlet line, where the first inlet line provides unheated water to the first tank, and where the first outlet line draws heated water from the first tank. The system can also include a first tankless water heater having a second outlet line, where the second outlet line of the first tankless water heater provides the heated water to a first heated water demand. The system can also include a first valve that controls an amount of the unheated water flowing through the first inlet line to the first tank-based water heater. The system can further include a controller operatively coupled to the first valve, where the controller controls a position of the first valve based on the first heated water demand and a first capacity of the first tankless water heater.

Thermal targeting technology is used to continuously adjust boiler target temperature to the minimum necessary to satisfy the required heating load. Responsive to and initiated by a first call for heat, boiler target temperature is reduced by a predetermined amount upon or subsequent to the call for heat. Once the boiler temperature reaches this new target, a call timer is activated. If demand for heat is satisfied before a time set point is reached, the system ceases providing additional heat energy until the next heat demand. Responsive to and initiated by a next call for heat, the boiler target temperature is again reduced by the predetermined amount upon or subsequent to this next call for heat. Each time the heat demand is satisfied within the predetermined time interval, the boiler target temperature is reduced. If heat demand is not satisfied, a thermal boost is provided at set time intervals until the call for heat is removed.

A method for detecting malfunction of an electric boiler, the method including: a) detecting over scale accumulation by the steps of: metering the boiler's heating cycle, being a time from activating the boiler by a thermostat thereof until deactivating the boiler by the thermostat; if the heating cycle is longer than a threshold, then indicating over accumulation of scale in the boiler; b) detecting a malfunction of insulation of the boiler, by the steps of: metering the boiler's cooling cycle, being a time from deactivating the boiler by a thermostat thereof until reactivating the boiler by the thermostat; if the cooling cycle is shorter than the threshold, then indicating malfunction of insulation of the boiler; thereby allowing indicating malfunction of said boiler only by metering the heating and cooling cycles of said boiler.

A room heater is operated on receiving an on-command from a thermostat when a detected temperature detected by a second room-temperature detector falls below a first reference temperature, and is stopped on receiving an off-command when the temperature detected by the second room-temperature detector is above a second reference temperature that is set higher than the first reference temperature or when the thermostat is manually operated to be switched off. A setting temperature for temperature control to be carried out when the on-command is received again is updated according to a difference between the set temperature and the temperature detected by the first room-temperature detector on receiving the off-command. When the off-command is received before passing a predetermined period of time after receiving the on-command, the updating of the set temperature is prohibited if the temperature detected by the first room-temperature detector is below a predetermined minimum lower reference temperature.

A water heating system can include a water heater having a tank, an inlet line, and an outlet line, where the inlet line provides unheated water to the tank, and where the outlet line draws heated water from the tank. The water heating system can also include multiple sensing devices, where each sensing device of the plurality of sensing devices measures a parameter associated with the tank. The water heating system can further include a controller communicably coupled to the plurality of sensing devices, where the controller determines an amount of heated water in the tank based on measurements made by the plurality of sensing devices.