JP4286808B2 - Hot water heating system - Google Patents

Description

  The present invention relates to a hot water heating system including a heat source device having a heat exchanger heated by a burner, a heating radiator, and a circulation path for circulating hot water between the heat exchanger and the heating radiator.

  Conventionally, in this type of hot water heating system, the circulation path is divided into a forward passage for sending warm water heated by the heat exchanger to the heating radiator, and a return passage for returning the hot water that has passed through the heating radiator to the heat exchanger. The system is constructed, and a cistern and a circulation pump are interposed in the return passage. In the trial operation, the circulation pump is driven while supplying water to the circulation path via the systole to perform the deaeration operation for deaeration of the air in the circulation path (see, for example, Patent Document 1).

  By the way, recently, the number of heating radiators installed in homes is increasing, and it is necessary to increase the circulating flow rate of hot water in the circulation path. Here, in order to circulate a large flow rate of hot water through the circulation path via a heat exchanger having a large passage resistance, it is necessary to use a high-lift pump as a circulation pump. However, if a high circulation pump is used to secure a predetermined circulation flow rate in the circulation path, a considerable pressure is applied to the heat exchanger having a large passage resistance, causing a problem in terms of pressure resistance of the heat exchanger. In addition, in the heat exchanger, the flow path area is reduced, and when trying to secure the required circulation flow rate, the flow rate in the heat exchanger becomes very fast, causing an erosion phenomenon and deteriorating the durability of the heat exchanger. . Therefore, it is difficult to sufficiently increase the circulating flow rate of hot water in the circulation path in order to ensure the pressure resistance and durability of the heat exchanger.

  Therefore, the applicant of the present application previously made the circulation path into the first circulation path between the heat exchanger and the cistern and the second circulation path between the cistern and the heating radiator according to Japanese Patent Application No. 2004-247147. As a circulation pump, a hot water heating system including a first circulation pump that circulates hot water in a first circulation path and a second circulation pump that circulates hot water in a second circulation path has been filed. According to this, the circulation flow rate of the warm water for the heat exchanger is determined by the flow rate of the first circulation pump, and the circulation flow rate of the warm water for the heating radiator is determined by the flow rate of the second circulation pump. That is, the circulation flow rate for the heat exchanger and the circulation flow rate for the heating radiator can be determined individually, and even if the circulation flow rate for the heating radiator is increased, the circulation flow rate for the heat exchanger is relatively reduced, The pressure resistance and durability of the heat exchanger can be prevented from being adversely affected.

However, in the hot water heating system of the prior application, even when the first and second circulation pumps are driven while supplying water to both the first and second circulation paths via the systern during the trial operation, the first and second circulation pumps are used. This causes a problem that the air in each circulation path cannot be deaerated well. The cause is that, as a result of diligent efforts, the air pushed out from one of the first and second circulation paths to the cistern is re-sucked into the other circulation path, making it difficult for the air to escape out of the system. found.
Japanese Patent Laid-Open No. 63-75428 (pages 2, 3 and 1 and 4)

  In view of the above points, an object of the present invention is to provide a hot water heating system that can perform degassing of the first and second circulation paths in the above-mentioned prior application.

  In order to solve the above problems, the present invention comprises a heat source device having a heat exchanger heated by a burner, a heating radiator, and a circulation path for circulating hot water between the heat exchanger and the heating radiator. Warm water that performs deaeration operation that degass the air in the circulation path by driving the circulation pump while supplying water to the circulation path via the systern during the trial operation. In the heating system, the circulation path is divided into a first circulation path between the heat exchanger and the cistern and a second circulation path between the cistern and the heating radiator, and the first circulation is used as a circulation pump. The first circulation pump that circulates the hot water in the passage and the second circulation pump that circulates the hot water in the second circulation passage. In the deaeration operation, the air in the first circulation passage is driven by the first circulation pump. Degassing operation of the first circulation path for degassing the second circulation pump And the decirculation operation of the second circulation path for degassing the air in the second circulation path, and after the degassing operation of one of the first circulation path and the second circulation path is completed, Control means for performing deaeration operation of the circulation path is provided.

  According to the present invention, the first and second circulation pumps are not driven at the same time during the deaeration operation. Therefore, the first and second circulation pumps are pushed out from the first circulation path to the systern during the deaeration operation of the first circulation path. Air is sucked again into the second circulation path by the suction force of the second circulation pump, or air pushed out from the second circulation path into the systern during the deaeration operation of the second circulation path is caused by the suction force of the first circulation pump. It is possible to prevent re-suction to the first circulation path. Therefore, the air in each of the first and second circulation paths can easily escape to the outside of the system through the cistern, and the degassing of each circulation path can be performed satisfactorily.

  The total internal volume of the second circulation path including the heating radiator is much larger than that of the first circulation path, and a large amount of air is pushed out from the second circulation path to the systern during the deaeration operation of the second circulation path. There is a possibility that a part thereof will enter the first circulation path. Here, if the deaeration operation of the first circulation path is performed after the completion of the deaeration operation of the second circulation path, a part of the air pushed out from the second circulation path during the deaeration operation of the second circulation path is the first. Even if it enters one circulation path, air does not remain in the first circulation path in the subsequent deaeration operation of the first circulation path, which is advantageous.

  Referring to FIG. 1, reference numeral 1 denotes a heat source machine, which constitutes a hot water heating system that performs heating by circulating hot water heated by the heat source machine 1 to a heating radiator 2 such as a floor heating panel. The heat source device 1 is provided with a combustion housing 3, and a burner 4 and a heat exchanger 5 heated by the burner 4 are accommodated in the combustion housing 3. Combustion air is supplied into the combustion housing 3 by a combustion fan 6.

  A gas main valve 41 and a gas proportional valve 42 are interposed in the gas passage 40 for supplying fuel gas to the burner 4. The burner 4 is composed of a plurality of unit burners 4a. These unit burners 4a are divided into a plurality of sets, the gas passage 40 is branched downstream of the gas proportional valve 42 for each set of unit burners 4a, and fuel gas is supplied to each set of unit burners 4a in each branch path. A capacity switching valve 43 is provided. Thus, the combustion amount of the burner 4 can be varied over a wide range by combining the control of the capacity switching valve 43 and the control of the gas proportional valve 42.

  The heat exchanger 5 includes a main heat exchanger 51 disposed immediately above the burner 4 and a sub heat exchanger 52 disposed in an exhaust passage through which combustion exhaust gas that has passed through the main heat exchanger 51 flows. A sub heat exchanger 52 is connected in series on the upstream side of the exchanger 51. In the auxiliary heat exchanger 52, water vapor in the combustion exhaust is condensed and latent heat is recovered. Then, the condensed water is drained from the drain pipe 52c via the drain receiver 52a and the neutralizer 52b arranged immediately below the auxiliary heat exchanger 52.

  Further, the heat source device 1 is provided with a cistern 7. Then, the hot water is circulated between the heat exchanger 5 and the cistern 7 via the first circulation path 8, and the hot water is circulated between the cistern 7 and the heating radiator 2 via the second circulation path 9. I have to. A plurality of heating radiators 2 are connected in parallel to the second circulation path 9 via water flow valves 2a such as thermal valves, and the operation switches of the respective heating radiators 2 are turned on. In addition, warm water can be circulated to each heating radiator 2 by opening the water passage valve 2a.

  By the way, when the number of installation of the heat radiator 2 is large, it is necessary to considerably increase the total circulation flow rate of hot water with respect to the heat radiator 2. Here, the circulation path between the heat exchanger 5 and the heating radiator 2 is not divided into the first circulation path 8 and the second circulation path 9 as in this embodiment, and hot water for the heating radiator 2 is not divided. When hot water flows through the heat exchanger 5 at a flow rate equal to the circulation flow rate, if the circulation flow rate is increased, the pressure resistance and durability of the heat exchanger 5 are adversely affected. Therefore, in order to ensure the pressure resistance and durability of the heat exchanger 5, the total circulating flow rate of hot water with respect to the heating radiator 2 cannot be increased so much. On the other hand, in this embodiment, the hot water circulation flow rate for the heat exchanger 5 (hot water circulation flow rate in the first circulation path 8) and the hot water circulation flow rate for the heating radiator 2 (hot water circulation in the second circulation path 9). Flow rate) can be determined individually. Therefore, even if the total circulating flow rate of hot water for the heating radiator 2 is increased, the circulating flow rate of hot water for the heat exchanger 5 is made relatively small so that the pressure resistance and durability of the heat exchanger 5 are not adversely affected. Can be. That is, it becomes possible to increase the total circulating flow rate of hot water to the heating radiator 2 without being restricted by the pressure resistance and durability of the heat exchanger 5.

  Hereinafter, the cistern 7 and the first and second circulation paths 8 and 9 will be described in detail. The cistern 7 is replenished with water through a water supply pipe 70 provided with a water refill valve 71. Then, two water level electrodes 72 and 73 for detecting a low water level and a high water level are attached to the cistern 7, and a deaeration operation to be described later is controlled based on an on / off signal of the water level electrodes 72 and 73. Further, an overflow pipe 74 is connected to the cistern 7 so that the water level does not exceed a predetermined upper limit level.

  The first circulation path 8 returns the warm water from the cis turn 7 to the heat exchanger 5 (sub heat exchanger 52) and the forward passage 8a that sends the warm water that has passed through the heat exchanger 5 (main heat exchanger 51) to the cis turn 7. The return passage 8b includes a first circulation pump 10 interposed in the return passage 8b. The second circulation path 9 is composed of a forward passage 9a for sending warm water from the cis turn 7 to the heating radiator 2 and a return passage 9b for returning the warm water from the heating radiator 2 to the cis turn 7, and the second circulation pump is connected to the forward passage 9a. 11 is interposed. Further, a bypass passage 9 c that connects the upstream side and the downstream side of the second circulation pump 11 is provided in the forward passage 9 a of the second circulation path 9. According to this, even when the flow of hot water from the return passage 9a to the return passage 9b is interrupted due to some abnormality during the operation of the second circulation pump 11, the second circulation pump 11 is connected to the second circulation pump 11 via the bypass passage 9c. The required amount of hot water flows through the circulation of the hot water, and the second circulation pump 11 is protected. Each of the first and second circulation pumps 10 and 11 is a variable flow rate pump driven by a DC motor.

  In the cis turn 7, in order to prevent the low temperature hot water returned to the cis turn 7 from the return passage 9 b of the second circulation path 9 from flowing into the forward passage 9 a of the second circulation path 9, the second circulation path 9 A baffle plate 75 is provided between the connecting portion of the forward passage 9a and the connecting portion of the return passage 9b. Further, in the present embodiment, the downstream end of the forward passage 8 a of the first circulation path 8 and the upstream end of the forward passage 9 a of the second circulation path 9 are joined and connected to the cistern 7. Therefore, when the hot water circulation flow rate in the second circulation path 9 is larger than the hot water circulation flow rate in the first circulation path 8, all of the hot water heated by the heat exchanger 5 does not pass through the cistern 7. Furthermore, the amount of heat supplied to the heating radiator 2 from the outgoing passage 8a of the first circulation path 8 through the outgoing passage 9a of the second circulation path 9 and added to the hot water by the heat exchanger 5 is efficiently increased. Is transmitted to. When the hot water circulation flow rate in the second circulation path 9 is smaller than the hot water circulation flow rate in the first circulation path 8, the hot water circulation flow rate in the second circulation path 9 among the hot water heated by the heat exchanger 5. The portion exceeding the flow amount flows into the cistern 7, and a part of the amount of heat added to the hot water by the heat exchanger 5 is transmitted to the cistern 7. As a result, the temperature of the hot water returned to the heat exchanger 5 rises, the amount of combustion of the burner 4 decreases, and energy efficiency is maintained favorably. In addition, the downstream end of the forward passage 8a of the first circulation path 8 and the upstream end of the forward passage 9a of the second circulation path 9 are individually connected to the cistern 7, and the hot water heated by the heat exchanger 5 is connected to the cistern 7. It is also possible to flow to the forward passage 9a of the second circulation path 9 via the route.

  The first circulation path 8 is provided with a first circulation path temperature sensor 12 for detecting the temperature of the hot water sent from the heat exchanger 5, and the second circulation path 9 has a forward path 9 a. A second circulation path temperature sensor 13 for detecting the temperature of the hot water supplied to the heating radiator 5 is provided.

  The heat source unit 1 is provided with a controller 14 as a control means, and when the operation switch of any one of the heating radiators 2 is turned on, the controller 14 causes both the first and second circulation pumps 10 and 11 and the combustion fan. 6 and the rotation of the combustion fan 6 is detected, the gas source valve 41 is opened, and a spark discharge is performed by a spark plug (not shown) to ignite the burner 4. When the combustion of the burner 4 is started in this way, the control of the gas proportional valve 42 and the capacity switching valve 43 based on the temperature detected by the second circulation path temperature sensor 13 is performed, and the second circulation path temperature sensor. The combustion amount of the burner 4 is controlled so that the detected temperature 13 is maintained at a predetermined set temperature. In the initial stage of operation, the number of revolutions of the first circulation pump 10 is lowered, and the hot water in the first circulation path 8 is set so that the temperature detected by the first circulation path temperature sensor 12 is equal to or higher than a predetermined temperature (for example, 60 ° C.). Reduce the circulating flow rate. Thereby, dew condensation in the main heat exchanger 5a can be prevented. Moreover, the rotation speed of the 2nd circulation pump 11 is controlled so that the warm water circulation flow rate in the 2nd circulation path 9 may change according to the operating number of the heating radiator 2, and coexistence with heating capability and energy-saving property is aimed at.

  Incidentally, a test run switch (not shown) is attached to the controller 14. When the trial operation switch is turned on after the hot water heating system is installed, the first and second circulation pumps 10 and 11 are driven while supplying water to the first and second circulation paths 8 and 9 via the systern 7. Thus, a deaeration operation for deaerating the air in the first and second circulation paths 8 and 9 is performed. The control of the deaeration operation by the controller 14 is as shown in FIG. 2, and this control will be described in detail below.

  In the deaeration operation control, first, the water flow valves 2a of all the heating radiators 2 are opened in the step S1, the supplementary water valve 71 is opened in the step S2, and the low water level is then opened in the step S3. It is determined whether or not the electrode 72 is in an on state (the low water level electrode 72 is in an on state when the water level in the cistern 7 is higher than the lower end of the low water level electrode 72). When the low water level electrode 72 is turned on by supplying water to the cistern 7 through the rehydration valve 71, the second circulation pump 11 is driven in step S4, and then again in the step S6. It is determined whether 72 is in an ON state.

  When the second circulation pump 11 is driven, the water in the cistern 7 is sent to the second circulation path 9 and the water level in the cistern 7 is initially lowered. As a result, the low water level electrode 72 is not determined to be in the ON state in step S6. In this case, the second circulating pump 11 is stopped in step S5, and then the process returns to step S3. The process is repeated. Each time the second circulation pump 11 is driven, the air in the second circulation path 9 is pushed out to the cistern 7, and the second circulation path 9 is gradually filled with water. Finally, even if the second circulation pump 11 is driven, the water level in the cistern 7 hardly decreases, and it is determined in step S6 that the low water level electrode 72 is in the ON state. In this case, the process proceeds to step S7, where the high water level electrode 73 is in the on state (the high water level electrode 73 is in the on state when the water level in the cistern 7 is higher than the lower end of the high water level electrode 73). Determine whether or not. If the high water level electrode 73 is not in the on state, the process returns to the step of S6. When the high water level electrode 73 is in the on state, the process proceeds to the step of S8, and the auxiliary water valve 71 and the water flow valves 2a of all the heating radiators 2 Is closed, the second circulation pump 11 is stopped, and the first stage deaeration operation of the second circulation path 9 is completed.

  When the first stage deaeration operation of the second circulation path 9 is performed as described above, the air in the forward passage 9a and the return path 9b of the second circulation path 9 is almost deaerated, but in each heating radiator 2 Air may remain in the Therefore, the second stage degassing operation of the second circulation path 9 is performed in which water is individually passed through the plurality of heating radiators 2 and the air remaining in each heating radiator 2 is completely deaerated.

  In the second stage deaeration operation of the second circulation path 9, first, in step S9, the water flow valve 2a of one heating radiator 2 selected in accordance with a predetermined order is opened, and then, In step S10, it is determined whether or not the low water level electrode 72 is on. If the low water level electrode 72 is not in the ON state, the refill valve 71 is opened in step S11 and the process returns to step S10. When the low water level electrode 72 is in the on state, after the second circulation pump 11 is driven in step S12, it is determined again in step S14 whether the low water level electrode 72 is in the on state. If the low water level electrode 72 is not on, the second circulation pump 11 is stopped in step S13, and the process returns to step S10 via step S11. If it is determined in step S14 that the low water level electrode 72 is in the on state, the process proceeds to step S16 to determine whether the high water level electrode 73 is in the on state, and the high water level electrode 73 is turned on. If not, the refill valve 71 is opened in step S15 and the process returns to step S14.

  When the high water level electrode 73 is turned on, the refill valve 71 is closed in step S17 and the process proceeds to step S18, and a predetermined time (for example, 1 minute) has elapsed from the start of driving of the second circulation pump 11. It is determined whether or not. Then, the process returns to the step S10 until the predetermined time elapses, and when the predetermined time elapses, the second circulation pump 11 is stopped at the step S19. Next, in step S20, it is determined whether or not a predetermined time (for example, 1 minute) has elapsed since the stop of the second circulation pump 11, and when a predetermined time has elapsed since the stop of the second circulation pump 11, the step of S21. After adding 1 to the first counter value C1 whose initial value is zero, it is determined whether or not the first counter value C1 has become 5 in step S22. Until C1 = 5, the process returns to step S10 and the above processing is repeated. When C1 = 5, the process proceeds to step S23, the water flow valve 2a of the selected heating radiator 2 is closed, and the deaeration of the heating radiator 2 is completed. Next, in step S24, it is determined whether or not all the heating radiators 2 have been deaerated. If not, the process returns to step S9 and one heating radiator 2 to be selected next is selected. The water flow valve 2a is opened, and deaeration of the heating radiator 2 is started.

  In the present embodiment, when each heating radiator 2 is deaerated, the intermittent operation of the second circulation pump 11 in which the second circulation pump 11 is driven for a predetermined time and stopped for a predetermined time is repeated five times. During the stop of the second circulation pump 11, air escapes from the system 7, and bubbles in the second circulation path 9 gather, and the next circulation pump 11 is driven to generate bubbles 7. The air in the second circulation path 9 including the selected heating radiator 2 is surely deaerated by repeating the intermittent operation of the second circulation pump 11.

  If it is determined in step S24 that all the heating radiators 2 have been degassed, that is, if it is determined that the second stage degassing operation of the second circulation path 9 has been completed, then A deaeration operation of one circulation path 8 is performed. In this deaeration operation, first, in step S25, it is determined whether or not the low water level electrode 72 is in an ON state. If the low water level electrode 72 is not on, the water refill valve 71 is opened in step S26 and the process returns to step S25. When the low water level electrode 72 is in the on state, after driving the first circulation pump 10 in step S27, it is determined again in step S29 whether the low water level electrode 72 is in the on state.

  Here, when the first circulation pump 10 is driven, the water in the cistern 7 is sent to the first circulation path 8 and the water level in the cistern 7 is initially lowered. As a result, in step S29, the low water level electrode 72 is not determined to be in the ON state. In this case, after the first circulation pump 10 is stopped in step S28, the process returns to step S25 via step S26. The process from step S29 to step S29 is repeated. Each time the first circulation pump 10 is driven, the air in the first circulation path 8 is pushed out to the cistern 7, and the first circulation path 8 is gradually filled with water. Finally, even if the first circulation pump 10 is driven, the water level in the cistern 7 hardly decreases, and it is determined in the step S29 that the low water level electrode 72 is in the ON state. In this case, the process proceeds to step S31 to determine whether or not the high water level electrode 73 is in the on state. If the high water level electrode 73 is not in the on state, the replenishment valve 71 is opened in step S30 and S29 is performed. Return to the step.

  When the high water level electrode 73 is turned on, the refill valve 71 is closed in step S32 and the process proceeds to step S33, and a predetermined time (for example, 1 minute) has elapsed from the start of driving the first circulation pump 10. It is determined whether or not. Then, the process returns to the step S25 until the predetermined time elapses, and when the predetermined time elapses, the first circulation pump 10 is stopped at the step S34. Next, it is determined whether or not a predetermined time (for example, 1 minute) has elapsed since the stop of the first circulation pump 10 in step S35, and when a predetermined time has elapsed since the stop of the first circulation pump 10, the step of S36 After adding 1 to the second counter value C2 whose initial value is zero, it is determined whether or not the second counter value C2 has become 5 in the step of S37. Until C2 = 5, the process returns to step S25 to repeat the above process. When C2 = 5, the deaeration operation is completed.

  Thus, even in the deaeration operation of the first circulation path 8, the intermittent operation of the first circulation pump 10 in which the first circulation pump 10 is driven for a predetermined time and stopped for a predetermined time is repeated five times. The air inside is surely degassed.

  By the way, when the low water level electrode 72 is turned on by supplying water to the cistern 7 by opening the water refill valve 71, the first and second circulation pumps 10 and 11 are driven together to drive the first and second circulation pumps. It is also conceivable to perform the deaeration operation of both the circulation paths 8 and 9 simultaneously. However, in this case, the air pushed out from one of the first and second circulation paths 8 and 9 to the cistern 7 is re-sucked into the other circulation path, and the air is difficult to escape out of the system. The air in 8, 9 cannot be degassed well. On the other hand, in the present embodiment, the first and second circulation pumps 10 and 11 are not simultaneously driven during the deaeration operation. Therefore, the first circulation is performed during the deaeration operation of the first circulation path 8. The air pushed out from the path 8 to the cistern 7 is sucked into the second circulation path 9 again by the suction force of the second circulation pump 11, or from the second circulation path 9 to the cistern 7 during the deaeration operation of the second circulation path 9. It is possible to prevent the air pushed out to the first circulation path 8 due to the suction force of the first circulation pump 10. Therefore, the air in each of the first and second circulation paths 8 and 9 can easily escape to the outside of the system via the cistern 7, and the circulation paths 8 and 9 can be deaerated well.

  In the present embodiment, the second circuit 9 is first deaerated, but the first circuit 8 is first degassed, and then the second circuit 9 is degassed. It is also possible to do this. However, the total internal volume of the second circulation path 9 including the heating radiator 2 is much larger than that of the first circulation path 8, and the second circulation path 9 is changed from the second circulation path 9 to the cistern 7 during the deaeration operation of the second circulation path 9. A large amount of air is pushed out, and a part of the air may enter the first circulation path 8. Considering this, it is desirable to perform the deaeration operation of the first circulation path 8 after the completion of the deaeration operation of the second circulation path 9 as in the present embodiment. That is, even if a part of the air pushed out from the second circulation path 9 enters the first circulation path 8 during the deaeration operation of the second circulation path 9, the subsequent deaeration operation of the first circulation path 8 is performed. No air remains in the first circulation path 8.

  As mentioned above, although embodiment of this invention was described with reference to drawings, this invention is not limited to the thing of embodiment. For example, in the above embodiment, the heat exchanger 5 includes the main heat exchanger 51 and the sub heat exchanger 52, but the sub heat exchanger 52 may be omitted. In the above embodiment, both the first and second circulation pumps 10 and 11 are constituted by variable flow rate pumps that are driven by a DC pump. It is also possible to configure with a constant flow pump driven by an AC motor.

Explanatory drawing which shows the structure of the hot water heating system of embodiment of this invention. The flowchart which shows the content of the deaeration operation control performed with the hot water heating system of embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Heat source machine, 2 ... Heating radiator, 4 ... Burner, 5 ... Heat exchanger, 7 ... Systurn, 8 ... 1st circuit, 9 ... 2nd circuit, 10 ... 1st circulation pump, 11 ... 2nd Circulation pump, 14... Controller (control means).

Claims (2)

A heat source unit having a heat exchanger heated by a burner, a heating radiator, and a circulation path for circulating hot water between the heat exchanger and the heating radiator are provided. It is a hot water heating system that performs a deaeration operation to deaerate the air in the circulation path by driving the circulation pump while supplying water to the circulation path via a systern during the trial operation,
The circulation path is divided into a first circulation path between the heat exchanger and the cistern and a second circulation path between the cistern and the heating radiator, and circulates hot water through the first circulation path as a circulation pump. In what has the 1st circulation pump and the 2nd circulation pump which circulates warm water to the 2nd circulation way,
In the deaeration operation, the first circulation path is deaerated by driving the first circulation pump, and the air in the second circulation path is deaerated by driving the second circulation pump. Divided into deaeration operation of the second circulation path,
A hot water heating system comprising control means for performing deaeration operation of the other circulation path after completion of the deaeration operation of one of the first circulation path and the second circulation path.   2. The hot water heating system according to claim 1, wherein the control unit is configured to perform the deaeration operation of the first circuit after the completion of the deaeration operation of the second circuit. 3.

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