Abstract: A water heater includes: a burner; a heat exchanger; a fan for supplying air to the burner and emitting combustion gas having passed through the heat exchanger to outside of the water heater; and a drainage water discharge path connected to the heat exchanger. The drainage water discharge path has a water-sealing structure that is water-sealed by drainage water. The water heater further includes a control unit: having a water-seal determination unit giving permission that the water heater can operate in a normal mode based on a condition that the drainage water discharge path has been water-sealed; and issuing an instruction to cause the burner to intermittently operate for a time period until the water-seal determination unit gives the permission.

Abstract: A fan serves to suction combustion gas which has passed through a secondary heat exchanger and emitting combustion gas to the outside of a water heater. A drainage water discharge pipe is connected to the secondary heat exchanger in order to discharge the drainage water produced as a result of recovery of latent heat in the secondary heat exchanger to the outside of the secondary heat exchanger. An air passage pipe is connected to an exhaust box. A Y-shaped pipe joint has a flow path allowing merging of the drainage water discharge pipe and the air passage pipe, and the flow path after merging leads to the outside of the water heater.

Abstract: A water heater includes: a burner; a heat exchanger; a fan for supplying air to the burner and emitting combustion gas having passed through the heat exchanger to outside of the water heater; and a drainage water discharge path connected to the heat exchanger. The drainage water discharge path has a water-sealing structure that is water-sealed by drainage water. The water heater further includes a control unit: having a water-seal determination unit giving permission that the water heater can operate in a normal mode based on a condition that the drainage water discharge path has been water-sealed; and issuing an instruction to cause the burner to intermittently operate for a time period until the water-seal determination unit gives the permission.

Abstract: A fan serves to suction combustion gas which has passed through a secondary heat exchanger and emitting combustion gas to the outside of a water heater. A drainage water discharge pipe is connected to the secondary heat exchanger in order to discharge the drainage water produced as a result of recovery of latent heat in the secondary heat exchanger to the outside of the secondary heat exchanger. An air passage pipe is connected to an exhaust box. A Y-shaped pipe joint has a flow path allowing merging of the drainage water discharge pipe and the air passage pipe, and the flow path after merging leads to the outside of the water heater.