Water heater

A water heater comprising:

• a combustor for production of flue gas;
• a primary heat exchanger including a tank and at least one flue, the tank including a primary water inlet, a hot water outlet, and a two-way port;
• a secondary heat exchanger including a core and a flue gas flow path, the secondary heat exchanger including a secondary water inlet, and a secondary water outlet communicating with the primary water inlet so the tank receives water from the secondary heat exchanger;
• a tee defining a cold water inlet communicating with a source of cold water, the two-way port, and a secondary tee port communicating with the secondary water inlet;
• and
• a water pump operable to pump water to the secondary water inlet from the secondary tee port,
• wherein the water heater is operable in a heating mode in which the combustor produces flue gas and the water pump flows water from the tee through the core of the secondary heat exchanger and into the tank via the primary water inlet, and in a non-heating mode in which the combustor and the water pump are inoperative,
• wherein, in the heating mode, the flue gas flows from the combustor through the at least one flue to heat the water in the tank and then through the flue gas flow path to heat water in the core before being exhausted,
• wherein upon demand water is drawn out of the tank via the hot water outlet and replacement cold water from the source of cold water replaces hot water drawn from the tank, wherein at least some of the replacement cold water flows through the two-way port into the tank without flowing through the secondary heat exchanger.