A water heater has a primary heat exchanger having a first heat transfer tube, a secondary heat exchanger having a second heat transfer tube connected with the first heat transfer tube and being located higher than the first heat transfer tube, and an outflow path connected to an outflow-side end portion of the first heat transfer tube. The outflow path has an offset flow path portion including a rising portion which rises upward or obliquely upward from a connecting portion of the outflow path and the outflow-side end portion of the first heat transfer tube or from the vicinity of the connecting portion, the offset flow path portion being offset at a position higher than the outflow-side end portion. When hot water supply is temporally stopped, the water at high temperature in the first heat transfer tube flows into the offset flow path portion, thereby inhibiting such a disadvantage that water having a lower temperature than a target temperature is supplied because of a natural convection at the time of restarting hot water supply.

A water heater has a primary heat exchanger having a first heat transfer tube, a secondary heat exchanger having a second heat transfer tube connected with the first heat transfer tube and being located higher than the first heat transfer tube, and an outflow path connected to an outflow-side end portion of the first heat transfer tube. The outflow path has an offset flow path portion including a rising portion which rises upward or obliquely upward from a connecting portion of the outflow path and the outflow-side end portion of the first heat transfer tube or from the vicinity of the connecting portion, the offset flow path portion being offset at a position higher than the outflow-side end portion. When hot water supply is temporally stopped, the water at high temperature in the first heat transfer tube flows into the offset flow path portion, thereby inhibiting such a disadvantage that water having a lower temperature than a target temperature is supplied because of a natural convection at the time of restarting hot water supply.

A combustion device includes a combustion control section which controls combustion in the combustion device; a setting section operated to set information indicating whether or not a plurality of combustion devices are in a common vent discharge state; and a memory section which stores therein connection configurations with the other combustion control sections to which the combustion control section is communicatively connected, and the combustion control section determines whether or not the combustion control section can communicate with a linkage control section or the other combustion control sections, and inhibits combustion in the combustion device to which the combustion control section belongs, in a case where the combustion control section determines that the combustion control section cannot communicate with the linkage control section or at least one of the other combustion control sections and the common vent discharge state is set by the setting section.

A water heater system including a boiler having a heat exchanger and an indirect water heater having a heat exchanger, and a controller configured to activate a pump such that the water flows between the boiler heat exchanger and the indirect water heater heat exchanger, and to control a heat source to provide heat to the boiler at a firing rate. The water heater system measuring temperatures of the water at the boiler water inlet and at the boiler water outlet, calculating an amount of heat transfer from the boiler heat exchanger to the indirect water heater exchanger based on the measured temperatures, and adjusting the firing rate based on the calculated amount of heat transfer to determine a heat transfer capacity of the indirect water heater exchanger.