JP2021094526A - Water heater - Google Patents

Abstract

To provide a water heater which is advantageous in preventing flow path components forming a bath water circulation path from being degraded by ultraviolet rays of a sterilization device.SOLUTION: A sterilization device 13 includes an inlet 18 through which bath water flows into a treatment space 17a of an enclosure 17, an outlet 19 through which bath water flows out of the treatment space 17a, and a UV radiation part 30 which irradiates the bath water in the treatment space 17a with UV light. The water heater is equipped with a UV-resistant fitting 20 which is connected to at least one bath water port of the inlet 18 and the outlet 19. The fitting 20 has one end 20a connected to the bath water port and the other end connected to flow path components forming a bath water circulation path. The cross-sectional area of the flow path of the fitting 20 is greater than or equal to the cross-sectional area of the flow path of the bath water port. The fitting 20 has a bent part 20c where the flow path is bent. The ultraviolet rays U made incident from the treatment space 17a to the inside of the fitting 20 hit an inner wall 20c of the bent part, preventing the ultraviolet rays U from directly irradiating the flow channel components.SELECTED DRAWING: Figure 3

Description

This disclosure relates to a water heater.

In order to suppress the increase of various bacteria that propagate in the bathtub during or after bathing, it is equipped with a sterilization device that sterilizes the bath water by irradiating the bath water flowing in from the bathtub through the bath water circulation route with ultraviolet rays. Water heaters are known. The liquid purification treatment apparatus disclosed in Patent Document 1 below surrounds a container having an inlet of the liquid to be treated and an outlet of the treated liquid, an ultraviolet radiation lamp arranged in the container, and the inlet and the outlet. It is provided with a resin joint and a tubular attachment portion forming a fastening portion on the inner peripheral surface, which is formed on the outer side of the container as described above. The attachment has an inner diameter larger than the corresponding inlet or outlet diameter.

Japanese Unexamined Patent Publication No. 2015-139711

The liquid purification treatment apparatus of Patent Document 1 has the following problems. Since the diameter of the inlet or outlet is smaller than the inner diameter of the mounting portion, it becomes a throttle portion and pressure loss occurs. Further, it is possible to prevent the ultraviolet rays radiated from the ultraviolet radiation lamp in the direction perpendicular to the lamp axis from being irradiated to the fastening portion, but it is possible to prevent the ultraviolet rays from being irradiated to the portion of the joint other than the fastening portion. Can not. Further, it is not possible to prevent the ultraviolet rays emitted from the ultraviolet emitting lamp in a direction other than the direction perpendicular to the lamp axis from being irradiated to the joint including the fastening portion. For these reasons, it is not possible to sufficiently prevent the resin joint from being deteriorated by ultraviolet rays.

The present disclosure has been made to solve the above-mentioned problems, and provides a water heater that is advantageous in preventing the flow path components forming the bath water circulation path from being deteriorated by the ultraviolet rays of the sterilizer. The purpose is to do.

The water supply machine according to the present disclosure is a water supply machine provided with a sterilization device for sterilizing bath water flowing in from a bathtub through a bath water circulation path, and the sterilization device forms a treatment space through which bath water flows. It is equipped with a housing, an inlet through which bath water flowing into the treatment space passes, an outlet through which bath water flowing out of the treatment space passes, and an ultraviolet irradiation unit that irradiates the bath water in the treatment space with ultraviolet rays. The machine is connected to at least one of the inlet and outlet of the bath and is equipped with a UV resistant joint, which is attached to one end connected to the outlet and a flow path component forming a bath water circulation path. With the other end connected, the flow path cross-sectional area of the joint is greater than or equal to the flow path cross-sectional area of the bath water port, and the joint has a bent portion where the flow path is bent, from the processing space to the inside of the joint. By hitting the inner wall of the bent portion with the incident ultraviolet rays, the ultraviolet rays are prevented from being directly applied to the flow path components.

According to the present disclosure, it is possible to provide a water heater that is advantageous in preventing the flow path components forming the bath water circulation path from being deteriorated by the ultraviolet rays of the sterilizer.

It is a front view which shows the water heater by Embodiment 1. FIG. It is a schematic diagram which shows the structure of the inside of the hot water storage unit of the water heater and the bathtub by Embodiment 1. It is sectional drawing of the sterilization apparatus, the 1st joint, and the 2nd joint provided in the water heater according to Embodiment 1. FIG. It is a cross-sectional view which expanded a part of FIG.

Hereinafter, embodiments will be described with reference to the drawings. The elements common to or corresponding to each other in the drawings are designated by the same reference numerals to simplify or omit the description. In the following description, the description of "water" means, in principle, liquid water, and may include low-temperature water to high-temperature hot water.

Embodiment 1.
FIG. 1 is a front view showing the water heater 1 according to the first embodiment. As shown in FIG. 1, the water heater 1 of the present embodiment is a hot water storage type water heater including a heat pump unit 2 and a hot water storage unit 3. The heat pump unit 2 is an example of a heating means for heating water. The heat pump unit 2 and the hot water storage unit 3 are connected by a heat pump forward pipe 4, a heat pump return pipe 5, and electrical wiring (not shown). The low-temperature water before heating is sent from the hot water storage unit 3 to the heat pump unit 2 through the heat pump going pipe 4. The high-temperature water heated by the heat pump unit 2 returns to the hot water storage unit 3 through the heat pump return pipe 5 and is stored. The hot water storage unit 3 is connected to the bathtub 100 installed in the bathroom via the bath going pipe 7 and the bath returning pipe 8. In the following description, the hot water stored in the bathtub 100 is referred to as "bath water". The bath going pipe 7 and the bath returning pipe 8 form a part of the bath water circulation path 6 which is a path through which bath water circulates between the bathtub 100 and the hot water storage unit 3. In the illustrated configuration, the heat pump unit 2 and the hot water storage unit 3 are separate bodies, but the water heater according to the present disclosure may be a combination of the heat pump unit 2 and the hot water storage unit 3. Further, the water heater according to the present disclosure is not limited to the hot water storage type water heater, and can be applied to the instantaneous water heater.

FIG. 2 is a schematic view showing the inside of the hot water storage unit 3 of the water heater 1 and the configuration of the bathtub 100 according to the first embodiment. As shown in FIG. 2, a hot water storage tank 9 is installed in the hot water storage unit 3. In the following description, the hot water stored in the hot water storage tank 9 is referred to as "tank water". The hot water storage unit 3 is further provided with a tank water pump 10, a bath water heat exchanger 11, a bath water pump 12, and a sterilization device 13. The bath water heat exchanger 11 has a primary side flow path 11a through which tank water passes and a secondary side flow path 11b through which bath water passes. The inlet of the primary side flow path 11a is connected to the hot water storage tank 9 via the flow path 14. A tank water pump 10 is connected in the middle of the flow path 14. The outlet of the primary side flow path 11a is connected to the hot water storage tank 9 via the flow path 15. When the tank water pump 10 operates, the tank water flowing out of the hot water storage tank 9 circulates so as to return to the hot water storage tank 9 through the flow path 14, the tank water pump 10, the primary side flow path 11a, and the flow path 15.

The downstream end of the bath return pipe 8 is connected to the suction port of the bath water pump 12. The discharge port of the bath water pump 12 is connected to the inlet of the secondary side flow path 11b via the flow path 16. When the bath water pump 12 operates, the bath water flowing out of the bathtub 100 flows into the secondary side flow path 11b through the bath return pipe 8, the bath water pump 12, and the flow path 16. The bath water that has passed through the secondary side flow path 11b flows into the sterilizing device 13. The bath water that has passed through the sterilizing device 13 returns to the inside of the bathtub 100 through the bath going pipe 7. The bath water pump 12, the flow path 16, and the secondary side flow path 11b form a part of the bath water circulation path 6.

In the present embodiment, the tank water pump 10 and the bath water pump 12 are operated to exchange heat between the tank water and the bath water in the bath water heat exchanger 11, so that the reheating operation of the bath water 100 is performed. Alternatively, a heat recovery operation can be performed to recover the heat of the remaining hot water in the bathtub 100 into the hot water storage tank 9. In FIG. 2, the heat pump forward pipe 4 and the heat pump return pipe 5 are not shown. In addition, the operation of the water supply pipe through which water supplied from a water source such as a water supply passes, the hot water supply pipe for supplying hot water to the hot water supply destination such as the bathtub 100, the faucet, and the shower, the mixing valve for adjusting the hot water supply temperature, and the operation of the water heater 1. Equipment such as a control device for controlling is further provided in the hot water storage unit 3, but the illustration of these equipment is also omitted.

The sterilizer 13 sterilizes the bath water by irradiating the bath water flowing from the bathtub 100 through the bath water circulation path 6 with ultraviolet rays. As a result, it is possible to suppress an increase in various bacteria that may propagate in the bathtub 100 during or after bathing. The water supply machine 1 may sterilize the bath water by the sterilizing device 13 during the reheating operation or the heat recovery operation, or sterilize while operating the bath water pump 12 without operating the tank water pump 10. The sterilization operation for sterilizing the bath water by the device 13 may be executed separately from the reheating operation and the heat recovery operation.

FIG. 3 is a cross-sectional view of the sterilization device 13, the first joint 20, and the second joint 21 included in the water heater 1 according to the first embodiment. As shown in FIG. 3, the sterilizer 13 includes a housing 17 forming a treatment space 17a through which bath water flows, an inflow port 18 through which bath water flowing into the treatment space 17a passes, and a bath flowing out from the treatment space 17a. An outlet 19 through which water passes and an ultraviolet irradiation unit 30 that irradiates the bath water in the treatment space 17a with ultraviolet rays are provided.

The housing 17 in the illustrated example has a rectangular cross-sectional shape, but the shape of the housing 17 is not limited to the illustrated example. The housing 17 has a first wall 17b and a second wall 17c located opposite to each other with the processing space 17a in between. The inflow port 18 projects outward from the outer surface of the first wall 17b. The outlet 19 projects outward from the outer surface of the second wall 17c. The virtual straight line extending the central axis of the inflow port 18 to the inside of the housing 17 intersects the second wall 17c. The virtual straight line extending the central axis of the outflow port 19 to the inside of the housing 17 intersects the first wall 17b and the ultraviolet irradiation unit 30.

In the illustrated example, the inflow port 18 and the outflow port 19 are integrally formed with the housing 17. As a modification, the inflow port 18 and the outflow port 19 may be different parts from the housing 17. The housing 17, the inflow port 18, and the outflow port 19 are made of an ultraviolet resistant material described later.

The ultraviolet irradiation unit 30 includes an ultraviolet source. The ultraviolet source may be, for example, an ultraviolet lamp such as a mercury lamp, or an ultraviolet light emitting diode (LED). In the illustrated example, the ultraviolet irradiation unit 30 is fixed to the inner surface of the first wall 17b. Instead of the configuration in which the ultraviolet irradiation unit 30 is arranged inside the housing 17 as shown in the illustrated example, the ultraviolet irradiation unit 30 is arranged outside the housing 17, and a window having ultraviolet transmission is provided in the housing 17. The ultraviolet rays emitted from the ultraviolet irradiation unit 30 may be transmitted through the window and irradiated to the bath water in the treatment space 17a. The ultraviolet ray U in FIG. 3 shows an example of the path of the ultraviolet ray emitted from the ultraviolet ray irradiating unit 30 into the processing space 17a.

The first joint 20 is made of a material having ultraviolet resistance. For example, the first joint 20 may be made of a metal material such as copper or stainless steel. Further, the first joint 20 is deteriorated by ultraviolet rays such as a fluororesin such as PTFE (polytetrafluoroethylene) and PFA (perfluoroalkoxy alkane), an acrylic resin such as PMMA (polymethylmethacrylate resin), and polycarbonate. It may be made of a resin material that is difficult to handle. Further, the first joint 20 may be made by using a resin material containing an additive for protecting from ultraviolet rays (for example, an ultraviolet absorber, a light stabilizer, etc.). The first joint 20 may be made by combining a plurality of ultraviolet resistant materials as described above. Since the first joint 20 has ultraviolet resistance, deterioration is surely suppressed even when exposed to ultraviolet rays from the ultraviolet irradiation unit 30.

The first joint 20 has one end 20a connected to the outlet 19. The first joint 20 forms a flow path for bath water that communicates with the outlet 19. Although not shown, the other end of the first joint 20 is connected to another flow path component forming the bath water circulation path 6. The flow path component may be, for example, a bath going pipe 7 or another joint. The flow path component may be made of an ordinary resin material that does not have ultraviolet resistance.

The first joint 20 has a first straight portion 20b, a bent portion 20c, and a second straight portion 20d. The first straight portion 20b forms a flow path that extends straight from one end 20a in the same direction as the central axis of the outlet 19. The bent portion 20c is between the first straight portion 20b and the second straight portion 20d. The bent portion 20c forms a curved flow path. The second straight portion 20d forms a flow path that extends straight from the bent portion 20c in a direction different from that of the first straight portion 20b. In the illustrated example, the central axis of the second straight portion 20d is orthogonal to the central axis of the first straight portion 20b. Instead of the illustrated example, the angle between the central axis of the second straight portion 20d and the central axis of the first straight portion 20b may be an obtuse angle or an acute angle.

In the present embodiment, the ultraviolet rays U incident on the inside of the first joint 20 from the processing space 17a hit the inner wall of the bent portion 20c and are blocked, so that the ultraviolet rays U are connected to the other end of the first joint 20. Direct irradiation of road components is prevented. As a result, it is possible to reliably prevent the flow path component from being deteriorated by ultraviolet rays. Further, since it is not necessary to make the flow path component from the ultraviolet resistant material, the cost of the flow path component can be suppressed.

Generally, inside the hot water storage unit 3, a pipe joint made of copper, stainless steel, or the like may be used to connect the parts. Such a pipe joint may be used as the first joint 20. In order to arrange the parts in the limited space in the hot water storage unit 3, such a pipe joint often requires a bent portion. Therefore, the first joint 20 provided with the bent portion 20c can be provided without increasing the manufacturing cost.

The second joint 21 has one end 21a connected to the inflow port 18. The second joint 21 forms a flow path for bath water that communicates with the inflow port 18. Although not shown, the other end of the second joint 21 is connected to another flow path component forming the bath water circulation path 6. For example, the other end of the second joint 21 may be connected to the outlet of the secondary side flow path 11b of the bath water heat exchanger 11.

In the present embodiment, the ultraviolet irradiation unit 30 is arranged so that the ultraviolet U emitted from the ultraviolet irradiation unit 30 is directly irradiated to the outlet 19. The ultraviolet rays U emitted from the ultraviolet irradiation unit 30 reach the flow path in the outlet 19 and the flow path in the first straight portion 20b. Therefore, the ultraviolet rays U are irradiated not only to the bath water flowing through the treatment space 17a but also to the bath water flowing through the flow path in the outlet 19 and the flow path in the first straight portion 20b. As a result, the bath water is exposed to the ultraviolet rays U for a long time, so that the sterilization effect can be improved. The ultraviolet irradiation unit 30 may be arranged so that the optical axis of the ultraviolet U emitted from the ultraviolet irradiation unit 30 passes through the flow path in the outlet 19 and the flow path in the first straight portion 20b.

In the present embodiment, the ultraviolet irradiation unit 30 is arranged so that the ultraviolet U emitted from the ultraviolet irradiation unit 30 is not directly irradiated to the inflow port 18. Therefore, the ultraviolet U does not directly enter the inside of the second joint 21 from the ultraviolet irradiation unit 30. The second joint 21 does not have a bent portion in which the flow path is bent. In the present embodiment, since the ultraviolet U does not directly enter the inside of the second joint 21 from the ultraviolet irradiation portion 30, even if the second joint 21 having no bent portion is used, the second joint 21 It is possible to reliably prevent the ultraviolet rays U from hitting the flow path component connected to the other end. By using the second joint 21 having no bent portion, the cost of the second joint 21 can be reduced. In the present embodiment, a partition wall 31 is provided in the processing space 17a to separate the inflow port 18 and the ultraviolet irradiation unit 30. By blocking the ultraviolet rays U emitted from the ultraviolet irradiation unit 30 by the partition wall 31, it is possible to more reliably prevent the ultraviolet rays U from being directly irradiated to the inflow port 18. The partition wall 31 in the illustrated example projects from the inner surface of the first wall 17b between the inflow port 18 and the ultraviolet irradiation unit 30 toward the central portion of the processing space 17a.

In the illustrated example, the outlet 19 corresponds to the first bath outlet and the inlet 18 corresponds to the second bath outlet. Contrary to the illustrated example, the ultraviolet U emitted from the ultraviolet irradiation unit 30 is directly irradiated to the inflow port 18, and the ultraviolet U emitted from the ultraviolet irradiation unit 30 is not directly irradiated to the outlet 19. The ultraviolet irradiation unit 30 may be arranged. In that case, the first joint 20 is connected to the inflow port 18 corresponding to the first bath water port, and the second joint 21 is connected to the outflow port 19 corresponding to the second bath water port.

Further, instead of the illustrated example, the ultraviolet irradiation unit 30 may be arranged so that the ultraviolet U emitted from the ultraviolet irradiation unit 30 is directly irradiated to both the inflow port 18 and the outflow port 19. In that case, it is desirable to connect the first joint 20 to both the inflow port 18 and the outflow port 19.

The sterilization device 13 includes a joint attachment portion 22 to which the first joint 20 is attached, and a joint attachment portion 23 to which the second joint 21 is attached. The joint mounting portion 22 is a tubular portion connected to the tip of the outlet 19. The joint mounting portion 22 has an inner diameter and an outer diameter larger than those of the outlet 19. The inner diameter of the joint mounting portion 22 is larger than the outer diameter of the first joint 20. One end 20a of the first joint 20 is inserted into the joint mounting portion 22. The first joint 20 is fixed to the joint mounting portion 22 by the fixture 24. The joint mounting portion 23 is a tubular portion connected to the tip of the inflow port 18. The joint mounting portion 23 has an inner diameter and an outer diameter larger than those of the inflow port 18. The inner diameter of the joint mounting portion 23 is larger than the outer diameter of the second joint 21. One end 21a of the second joint 21 is inserted into the joint mounting portion 23. The second joint 21 is fixed to the joint mounting portion 23 by the fixture 25. The fixture 24 and the fixture 25 may be, for example, quick fasteners. With the above configuration, the first joint 20 and the second joint 21 can be reliably attached to the sterilizer 13 with a simple structure.

A reflection region that reflects ultraviolet rays may be formed on at least a part of the inner wall surface of the first joint 20. The sterilization efficiency can be further improved by irradiating the bath water with the ultraviolet rays reflected by the reflection region again. The reflective region is formed of a material having high ultraviolet reflectance. The material is hereinafter referred to as "ultraviolet reflective material". Examples of the ultraviolet reflective material include the above-mentioned fluorine-based resin, metal materials such as stainless steel, and the like. Ultraviolet rays incident on the inner wall surface of the bent portion 20c are easily reflected because the angle between the bent portion 20c and the inner wall surface may be close to vertical. Therefore, by forming a reflective region on the inner wall surface from one end 20a of the first joint 20 to the bent portion 20c, ultraviolet rays can be efficiently reflected, and the sterilization efficiency can be further improved.

FIG. 4 is an enlarged cross-sectional view of a part of FIG. As shown in FIG. 4, the inner diameter D1 of the first joint 20 is larger than the inner diameter D2 of the outlet 19. Therefore, the flow path cross-sectional area of the first joint 20 is larger than the flow path cross-sectional area of the outflow port 19. In the present embodiment, since the throttle portion in which the flow path is narrowed is not formed at the connection portion between the outlet 19 and the first joint 20, it is possible to reliably avoid a decrease in the flow rate due to the pressure loss. According to the present embodiment, both deterioration due to ultraviolet rays of the flow path component forming the bath water circulation path 6 and decrease in the flow rate of the bath water due to pressure loss can be reliably prevented. In the illustrated example, the diameter of the opening at one end 20a of the first joint 20 is equal to the inner diameter D1.

The cross-sectional shape of the flow path of the outlet 19 may be a shape other than a circle. Further, the cross-sectional shape of the flow path of the first joint 20 may be a shape other than a circle. Even in these cases, if the flow path cross-sectional area of the first joint 20 is equal to or larger than the flow path cross-sectional area of the outlet 19, the above-mentioned effect can be obtained. The flow path cross-sectional area is the area in the cross section perpendicular to the fluid flow direction.

The water heater 1 includes an O-ring 26 that seals a gap between the joint mounting portion 22 and the first joint 20. The O-ring 26 is an example of a sealing member. The O-ring 26 is sandwiched between the inner peripheral surface of the joint mounting portion 22 and the outer peripheral surface of the first joint 20. By ensuring the liquidtightness by the O-ring 26, leakage of bath water from the gap between the joint mounting portion 22 and the first joint 20 is prevented. The O-ring 26 is made of an elastic material that is resistant to UV light. Examples of the elastic material having ultraviolet resistance include ethylene propylene rubber, chlorosulfonated polyethylene, butyl rubber, chloroprene rubber, silicone rubber, and fluororubber. Further, the O-ring 26 may be made by using an elastic material containing an additive for protecting from ultraviolet rays (for example, an ultraviolet absorber, a light stabilizer, etc.). In the present embodiment, by using a sealing member such as an O-ring 26 having ultraviolet resistance, deterioration of the sealing member due to ultraviolet rays from the sterilizing device 13 can be reliably suppressed. Further, in the present embodiment, since the O-ring 26 is used as the seal member, the connecting portion between the joint mounting portion 22 and the first joint 20 has a simple structure, which is advantageous in reducing the cost. .. However, in the present disclosure, a sealing member other than the O-ring 26 may be used.

Instead of the illustrated example, the inner diameter of the first joint 20 may be larger than the outer diameter of the joint mounting portion 22, and the joint mounting portion 22 may be inserted into the first joint 20. Even in that case, the same effect as the illustrated example can be obtained.

Further, since the structure of the connecting portion between the joint mounting portion 23 and the second joint 21 is the same as the structure of the connecting portion between the joint mounting portion 22 and the first joint 20, an enlarged cross-sectional view is omitted.

1 water supply machine, 2 heat pump unit, 3 hot water storage unit, 4 heat pump going pipe, 5 heat pump return pipe, 6 bath water circulation path, 7 bath going pipe, 8 bath return pipe, 9 hot water storage tank, 10 tank water pump, 11 bath water heat Exchanger, 11a primary side flow path, 11b secondary side flow path, 12 bath water pump, 13 sterilization device, 14 flow path, 15 flow path, 16 flow path, 17 housing, 17a treatment space, 17b first wall , 17c 2nd wall, 18 inlet, 19 outlet, 20 1st joint, 20a one end, 20b 1st straight part, 20c bent part, 20d 2nd straight part, 21 2nd joint, 21a one end, 22 joint mounting part , 23 Fittings, 24 Fixtures, 25 Fixtures, 26 O-Rings, 30 Ultraviolet Irradiation Parts, 31 Partitions, 100 Bathtubs

Claims (7)

A water heater equipped with a sterilization device that sterilizes the bath water that flows in from the bathtub through the bath water circulation route.
The sterilization device is
A housing that forms a treatment space through which bath water flows,
An inflow port through which the bath water flowing into the treatment space passes, and
An outlet through which the bath water flowing out of the treatment space passes, and
An ultraviolet irradiation unit that irradiates the bath water in the treatment space with ultraviolet rays,
With
The water heater is connected to at least one of the inlet and the outlet and includes a UV-resistant joint.
The joint has one end connected to the bath water port and the other end connected to a flow path component forming the bath water circulation path.
The flow path cross-sectional area of the joint is equal to or larger than the flow path cross-sectional area of the bath water port.
The joint has a bent portion with a curved flow path.
A water heater that prevents ultraviolet rays incident on the inside of the joint from the processing space from directly irradiating the flow path components by hitting the inner wall of the bent portion. The ultraviolet rays emitted from the ultraviolet irradiation unit are directly applied to the first bath water port, which is one of the inlet and the outlet, and the ultraviolet rays emitted from the ultraviolet irradiation unit are the inlet and the flow. The ultraviolet irradiation part is arranged so that the second bath water outlet, which is the other of the outlets, is not directly irradiated.
One end of the joint is connected to the first bath water port, and the joint is connected to the first bath water port.
The water heater according to claim 1, further comprising a second joint connected to the second bath water port and having no bent portion in which the flow path is bent. The sterilization device includes a joint attachment portion to which the joint is attached.
The inner diameter of the joint mounting portion is larger than the outer diameter of the joint,
The water heater according to claim 1 or 2, wherein the joint is inserted in the joint mounting portion. The sterilization device includes a joint attachment portion to which the joint is attached.
The inner diameter of the joint is larger than the outer diameter of the joint mounting portion,
The water heater according to claim 1 or 2, wherein the joint mounting portion is inserted in the joint. A seal member for sealing the gap between the joint mounting portion and the joint is provided.
The water heater according to claim 3 or 4, wherein the sealing member has ultraviolet resistance. The water heater according to claim 5, wherein the seal member is an O-ring. The water heater according to any one of claims 1 to 6, wherein a reflection region for reflecting ultraviolet rays is formed on at least a part of the inner wall surface of the joint.

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