1. Field of the Invention
The present invention relates to a circulation type hot water supply device that circulates hot water through a hot water supply heat exchanger of a water heater even during a stop of delivery of hot water, and has a function of diagnosing abnormalities of the heat exchanger at early stages.
2. Description of the Related Art
A conventional water heater comprises a hot water supply heat exchanger, a burner that heats water supplied to the heat exchanger from a water supply channel upstream of the heat exchanger, and delivered hot water temperature detection means for detecting a temperature of hot water fed from the heat exchanger to a hot water delivering channel downstream of the heat exchanger. A combustion amount of the burner is controlled so that a delivered hot water temperature detected by the delivered hot water temperature detection means reaches a set hot water temperature set by a remote controller.
Another conventional water heater comprises a flow rate sensor and a flow rate control valve provided in a water supply channel, and supplied water temperature detection means for detecting a temperature of water supplied through the water supply channel to a heat exchanger. In this water heater, a combustion amount required for increasing a delivered hot water temperature to a set hot water temperature is calculated from a deviation between a delivered hot water temperature detected by delivered hot water temperature detection means and a supplied water temperature detected by the supplied water temperature detection means, and a water supply amount detected by the flow rate sensor, and a combustion amount of a burner is controlled by feedforward control. If the delivered hot water temperature is not increased to the set hot water temperature even with a maximum combustion amount of the burner, the water supply amount is reduced by the flow rate control valve.
Immediately after opening of a hot water delivering tap connected to a hot water delivering channel, cold water remaining in the hot water delivering channel between the heat exchanger and the hot water delivering tap flows out from the hot water delivering tap, which causes discomfort to a user. A conventional circulation type hot water supply device for solving such a problem is also known. In such a hot water supply device, a downstream end of a hot water delivering channel is connected to a water supply channel, and a circulating pump that returns hot water fed from a heat exchanger to a hot water delivering channel to the heat exchanger through the water supply channel is provided in the hot water delivering channel. In this device, water is supplied to the heat exchanger by an operation of the circulating pump even after the hot water delivering tap is closed to stop delivery of hot water, thereby causing combustion of a burner. This allows a temperature of the hot water in the hot water delivering channel to be maintained at an appropriate temperature, and allows the hot water at the appropriate temperature to be delivered immediately after the opening of the hot water delivering tap.
In areas with high water hardness, CaCO3 or MgCO3 contained in water is deposited in a heat absorbing pipe of a heat exchanger, and a deposit easily adheres to an inner surface of the heat absorbing pipe. Adhesion of the deposit reduces heat exchange efficiency of the heat exchanger to make it difficult for combustion heat of a burner to be absorbed by water, thereby increasing a temperature of the heat exchanger itself. Repeating combustion in this state causes heat damage to the heat exchanger and thus causes leakage.
Japanese Patent Laid-Open No. 2003-254615 discloses a simple water heater that is not of a circulation type that can identify abnormalities of a heat exchanger at early stages based on an amount of increase of a detection temperature from delivered hot water temperature detection means after a hot water delivering tap is closed to stop combustion of a burner (so-called, an amount of delayed water temperature increase). If adhesion of a deposit to an inner surface of a heat absorbing pipe reduces heat exchange efficiency of the heat exchanger to increase a temperature of the heat exchanger itself as described above, the detection temperature from the delivered hot water temperature detection means is significantly increased after a stop of delivery of hot water. Thus, the presence of an abnormality can be determined when the amount of increase of the detection temperature from the delivered hot water temperature detection means after the stop of the delivery of hot water reaches a predetermined threshold value or more.
It is desired to identify abnormalities of a heat exchanger at early stages using such a technique in a circulation type hot water supply device. Some circulation type hot water supply devices always drive a circulating pump. In such a device, water is supplied to a heat exchanger by an operation of a circulating pump even after a hot water delivering tap is closed to stop combustion of a burner, thereby causing no delayed water temperature increase of the heat exchanger. Thus, even if a deposit adheres to an inner surface of a heat absorbing pipe, a detection temperature from delivered hot water temperature detection means is not increased after a stop of delivery of hot water, and abnormalities of the heat exchanger cannot be identified based on an amount of increase of the detected temperature.
In view of the above described circumstances, the present invention has an object to provide a circulation type hot water supply device that can reliably identify an abnormality of a heat exchanger when it occurs, such as adhesion of a deposit to an inner surface of a heat absorbing pipe.