US20160363348A1

US20160363348A1 - Method of controlling combustion apparatus

Info

Publication number: US20160363348A1
Application number: US15/176,415
Authority: US
Inventors: Hideo Okamoto
Original assignee: Rinnai Corp
Current assignee: Rinnai Corp
Priority date: 2015-06-11
Filing date: 2016-06-08
Publication date: 2016-12-15
Also published as: JP2017003196A

Abstract

A combustion apparatus having a burner, a combustion box, a combustion fan for supplying combustion air, and a regulator for regulating the amount of combustion fan, an inspection operation is performed in a state in which an operational quantity of the regulator (fan rotational speed) is kept at a maximum amount Nmax. When a deviation between a maximum set combustion amount YQmax corresponding to supply/exhaust resistances as detected in the inspection operation and an actually measured maximum combustion amount Qmax is outside an allowable range, a secondary inspection operation is performed by lowering the fan rotational speed down to a value Now which is lower than Nmax by a predetermined rate. Based on the rate of decrease of Qlow relative to Qmax as detected by the secondary inspection operation, computation is made of a fan rotational speed Nsat at which the burner combustion amount ceases to increase even if the fan rotational speed is increased. The upper limit value of fan rotational speed is then changed to Nsat.

Description

BACKGROUND

1. Technical Field
This invention relates to a method of controlling a combustion apparatus which is provided with: a burner; a combustion box containing therein an object that is heated by combustion gas from the burner (this “object” is hereinafter also referred to as a “to-be-heated object”); a combustion fan for supplying combustion air to the burner; at least one of an air supply tube communicated with a suction side of the combustion fan and an exhaust pipe communicated with an exhaust port of the combustion box; and a gas amount regulating means for regulating an amount of fuel gas supply to the burner.
2. Related Art
As long as a primary pressure of the fuel gas is normal, the fuel gas supply amount increases in proportion to an increase in an operational quantity (amount of manipulation) of the gas amount regulating means. Suppose that the operational quantity of the gas amount regulating means in which the fuel gas supply amount becomes maximum that is necessary for control purpose is defined as an upper limit value. Then the operational quantity of the gas amount regulating means is managed to be varied within a range below the upper limit value depending on the required combustion amount. However, if the primary pressure of the fuel gas becomes insufficient due, for example, to clogging in a gas pipe, and the like, the fuel gas supply amount will increase to a certain degree when the operational quantity of the gas amount regulating means is increased. Thereafter, the fuel gas supply amount ceases to increase even if the operational quantity of the gas amount regulating means is increased further.
As a solution, the following art is known. That is, when the difference between the burner combustion amount that can originally be obtained when the operational quantity of the gas amount regulating means is increased to the upper limit value (maximum set combustion amount) and the burner combustion amount that is detected in a state in which the operational quantity of the gas amount regulating means is at the upper limit value (actually measured maximum combustion amount) exceeds a predetermined allowable range, a judgment is made that the primary pressure of the fuel gas is insufficient. Then, there is obtained a saturated value which is a value of the operational quantity of the gas amount regulating means at which the burner combustion amount ceases to increase even if the operational quantity of the gas amount regulating means is increased. The upper limit value of the operational quantity of the gas amount regulating means is then changed to the obtained saturated value (see, for example, JP 1995-198129A).
By the way, as the gas amount regulating means, largely classified, there are the following two systems, i.e., one is of proportional valve system and the other is of zero governor system. In the proportional vale system, a proportional valve is interposed in a fuel gas supply passage so that the fuel gas supply amount is regulated by the proportional valve. In the zero governor system, on the other hand, a downstream end of the fuel gas supply passage is connected to the air suction passage on the upstream side of the combustion fan, and the zero governor which maintains the secondary pressure at the atmospheric pressure, is interposed in the fuel gas supply passage. In this arrangement, the suction negative pressure on the upstream side of the combustion fan varies in proportion to the rotational speed of the combustion fan (strictly speaking, the amount of air supply by the combustion fan). The fuel gas supply amount that is determined by the differential pressure between the atmospheric pressure, that is the secondary pressure of the fuel gas, and the suction negative pressure, varies in proportion to the rotational speed of the combustion fan.
Here, let us define whichever of the air supply tube and the exhaust pipe is disposed in the combustion apparatus, as an auxiliary tube. Then, in the gas amount regulating means of the proportional valve system, when the flow resistance through the auxiliary tube increases, the pressure rises in the combustion box having disposed therein the gas nozzle. Therefore, the amount of gas to be ejected from the gas nozzle decreases and consequently the burner combustion amount decreases. In the gas amount regulating means of the zero governor system, when the flow resistance through the auxiliary tube increases, the air supply amount becomes smaller than the normal amount that corresponds to the rotational speed of the combustion fan. As a consequence of decrease in the suction negative pressure, the fuel gas supply amount decreases and the burner combustion amount decreases.
However, conventionally no attention has been paid to the decrease in the burner combustion amount due to an increase in the flow resistance through the auxiliary tube. If the flow resistance through the auxiliary tube is large even in case the primary pressure of the fuel gas is normal, the difference between the maximum set combustion amount and the actually measured maximum combustion amount exceeds an allowable range. A judgment is then made that the primary pressure of the fuel gas is insufficient and, consequently, the upper limit value of operational quantity of the gas amount regulating means is unnecessarily lowered.

SUMMARY

In view of the above points, it is an advantage of this invention to provide a method of controlling a combustion apparatus in which there can be prevented unnecessary lowering, under the influence of the flow resistance through the auxiliary tube, in the upper limit value of the operational quantity of the gas amount regulating means.

Means for Solving the Problems

In order to solve the above-mentioned problems, this invention is a method controlling a combustion apparatus. The combustion apparatus comprises: a burner; a combustion box for disposing therein a to-be-heated object that is heated by combustion gas from the burner; a combustion fan for supplying combustion air to the burner; at least one of an air supply tube communicated with a suction side of the combustion fan, and an exhaust pipe communicated with an exhaust port of the combustion box; and a gas amount regulating means for regulating an amount of fuel gas supply to the burner. The method comprises: searching in advance for change characteristics of a maximum set combustion amount due to change in flow resistance through an auxiliary tube, where the maximum set combustion amount is defined to be such a burner combustion amount as will originally be obtainable when a primary pressure of the fuel gas is normal and when an operational quantity of the gas amount regulating means is at an upper limit value at which the fuel gas supply amount becomes maximum, and where the auxiliary tube is defined to be whichever of the air supply tube and the exhaust pipe the combustion apparatus is provided with; performing an inspection operation while operating the combustion apparatus in a state in which the operational quantity of the gas amount regulating means is kept at the upper limit value, in order to detect the flow resistance through the auxiliary tube and the burner combustion amount; obtaining, from the change characteristics, the maximum set combustion amount that corresponds to the flow resistance, as detected in the inspection operation, through the auxiliary tube; when a deviation between the maximum set combustion amount and the actually measured maximum combustion amount that is the burner combustion amount as detected in the inspection operation is outside a predetermined allowable range, performing a secondary inspection operation to obtain a saturated value which is such a value of the operational quantity of the gas amount regulating means as the burner combustion amount will cease to increase even if the operational quantity of the gas amount regulating means is increased; and changing the upper limit value of the operational quantity of the gas amount regulating means to the obtained saturated value.
According to this invention, even in case the flow resistance through the auxiliary tube is large although the primary pressure of the fuel gas is normal, thereby resulting in a decrease in the actually measured maximum combustion amount, a comparison is made between the set maximum combustion amount that corresponds to such a flow resistance through the auxiliary tube as was detected in the inspection operation and the actually measured maximum combustion amount. Therefore, the deviation between the two amounts falls within an allowable range. In this manner, the upper limit value of the operational quantity of the gas amount regulating means will not be changed in the secondary inspection operation. As a consequence, unnecessary lowering, under the influence of the flow resistance through the auxiliary tube, in the upper limit value of the operational quantity of the gas amount regulating means can be prevented.
In this invention, preferably, the inspection operation is performed at a time of trial operation after having placed in position the combustion apparatus. The method further comprises: when the flow resistance through the auxiliary tube as detected in the inspection operation is outside a predetermined reference range, displaying “auxiliary tube abnormal” which means that the auxiliary tube is abnormal; and when a deviation between the maximum set combustion amount that corresponds to the flow resistance through the auxiliary tube as detected in the inspection operation and the actually measured maximum combustion amount is within the allowable range, displaying “primary pressure normal” which means that the primary pressure of the fuel gas is normal. According to this arrangement, the person in charge of installing the combustion apparatus ready for use can advantageously discriminate as to whether there is a problem such as clogging to, and/or loose connection in, the auxiliary tube and the gas piping. If there is such a problem, the person in question can easily discriminate where the problem lies.
Further, in this invention, preferably, the secondary inspection operation is performed by detecting the burner combustion amount while operating the combustion apparatus in a state in which the operational quantity of the gas amount regulating means is lowered by a predetermined rate from the upper limit value. In this case, the saturated value can be computed based on the rate of decrease of the burner combustion amount as detected in the secondary inspection operation relative to the actually measured maximum combustion amount. Further, in this case, when the rate of decrease of the burner combustion amount as detected in the secondary inspection operation relative to the actually measured maximum combustion amount is below a predetermined threshold value, preferably displaying “primary pressure abnormal” is made to show that the primary pressure of the fuel gas is abnormal.
Further, in this invention, when the upper limit value of the operational quantity of the gas amount regulating means is changed to the saturated value, preferably displaying is made of the upper limit value which shows the changed upper limit value. According to this arrangement, even if the upper limit value of the operational quantity of the gas amount regulating means is changed low and consequently the heating capacity is lowered, the user is informed of the fact of lowering in the heating capacity. In this manner, the user can be prevented from mistaking the phenomenon for a mechanical trouble in the combustion apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an example of a combustion apparatus for carrying out the method of control according to an embodiment of this invention.

FIG. 2 is a flow chart showing the method of control according to the embodiment of this invention.

FIG. 3 is a graph showing the relationship between the operational quantity (rotational speed of a combustion fan) and the combustion amount of a gas amount regulating means.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

With reference to FIG. 1, reference numeral 1 denotes a closed type of housing of a combustion apparatus. Inside the housing 1 there are housed: a burner 2; a combustion box 4 containing therein a heat exchanger 3 for supplying hot water, the heat exchanger serving the purpose as an object that is heated by the combustion gas of the burner 2 (“to-be-heated object”); and a combustion fan 5 for supplying the burner 2 with combustion air. The combustion apparatus is provided, as tubes which are auxiliary with the combustion apparatus, with: an air supply tube 6 which is communicated with the suction side of the combustion fan 5 through an inner space of the housing 1; and an exhaust pipe 7 which is communicated with an exhaust port 4 a of the combustion box 4. The combustion apparatus is further provided with a gas amount regulating means 8 for regulating an amount of fuel gas supply to the burner 2; and a controller 9 which serves as a control means. The controller 9 has connected thereto a remote control unit 9 a.
The gas amount regulating means 8 is of a zero governor system which is arranged such: that a downstream end of a fuel gas supply passage 81 is connected to a venturi section 52 which is provided in an air suction passage 51 on an upstream side of the combustion fan 5; and that the fuel gas supply passage 81 has interposed therein a zero governor 82 which maintains the secondary pressure at atmospheric pressure. According to this arrangement, the suction negative pressure at the venturi section 52 varies in proportion to the rotational speed of the combustion fan 5 (strictly speaking, the amount of air supply by the combustion fan 5). Also the fuel gas supply amount to be determined by the differential pressure between the atmospheric pressure that is the secondary pressure of the fuel gas and the suction negative pressure varies in proportion to the rotational speed of the combustion fan 5. By means of the controller 9 computation is made of the combustion amount (required combustion amount) of the burner 2 required for delivering hot water at a set temperature from the heat exchanger 3. By controlling the rotational speed of the combustion fan 5 so as to obtain an air supply amount corresponding to the required combustion amount, the amount of fuel gas supply to the burner 2 is also adjusted to the amount corresponding to the required combustion amount.
By the way, if the primary pressure of the fuel gas is normal, the fuel gas supply amount, i.e., the combustion amount of the burner 2, will increase in proportion to the rotational speed of the combustion fan 5, as illustrated by line “a” in FIG. 3, until the rotational speed of the combustion fan 5, that is an operational quantity of the gas amount regulating means 8, reaches a predetermined upper limit value Nmax. On the other hand, if the primary pressure of the fuel gas becomes insufficient due, for example, to clogging in the gas pipe, etc., as illustrated by line “b” in FIG. 3, the combustion amount of the burner 2 ceases to increase any further, at a point where the combustion amount of the burner 2 has increased to a certain degree as a result of increase in the rotational speed of the combustion fan 5. Any further increase in the rotational speed of the combustion fan 5 will not increase the combustion amount. Suppose that the value of the rotational speed of the combustion fan 5 at which the combustion amount of the burner 2 ceases to increase despite the increase in the rotational speed of the combustion fan 5, is defined as a saturated value Nsat. Then, if the rotational speed of the combustion fan 5 is increased to a value exceeding the saturated value Nsat, the air supply amount becomes excessive, so that the combustion at the burner 2 becomes instable.
Suppose that such a combustion amount of the burner 2 as will originally be obtainable when the rotational speed of the combustion fan 5 is made to be an upper limit value Nmax is defined as a maximum set combustion amount, and that such a combustion amount of the burner 2 as will be detected when the rotational speed of the combustion fan 5 is made to be the upper limit value Nmax is defined as an actually measured maximum combustion amount of the burner 2. Then, it is conceivable to change the upper limit value of rotational speed of the combustion fan 5 to the saturated value Nsat, based on a judgment that the primary pressure of the fuel gas is insufficient when the deviation between the maximum set combustion amount and the actually measured maximum combustion amount is outside the predetermined allowable range. However, if the supply/exhaust resistances that are total ventilation resistances in the air supply tube 6 and in the exhaust pipe 7 increase, the air supply amount becomes smaller than the regular amount that corresponds to the rotational speed of the combustion fan 5. As a consequence of decrease in the suction negative pressure, the fuel gas supply amount will also decrease. Accordingly, if the supply/exhaust resistances are large even if the primary pressure of the fuel gas is normal, the difference between the maximum set combustion amount and the actually measured maximum combustion amount exceeds the allowable range. A judgement will thus be made that the primary pressure of the fuel gas is insufficient, and the upper limit value of the rotational speed of the combustion fan 5 will unnecessarily be lowered.
In order to eliminate this kind of disadvantages, the following arrangement has been made in this embodiment. In other words, suppose that the primary pressure of the fuel gas is normal and that such a combustion amount of the burner 2 as will originally be obtainable when the rotational speed of the combustion fan 5 is made to be the upper limit value Nmax is defined to be a maximum set combustion amount. Change characteristics of the maximum set combustion amount due to the change in the supply/exhaust resistances were studied and these change characteristics were stored in memory on the controller 9.
Then, as shown in FIG. 2, at the time of trial operation of the combustion apparatus after it has been placed in position, i.e., when a switch for trial operation is discriminated to have been pushed in STEP 1, the process proceeds to STEP 2, where (i.e., in STEP 2), while keeping the combustion apparatus in operation in a state in which the rotational speed of the combustion fan 5 is maintained at the upper limit value Nmax, an inspection operation is performed to detect the supply/exhaust resistances and the combustion amount of the burner 2. By the way, the supply/exhaust resistances can be computed by detecting the amount of air to flow through the combustion fan 5 based on electric current of the motor for the combustion fan 5, on the differential pressure between the internal pressure of the housing 1 and the suction negative pressure of the combustion fan 5, or the like. Further, the combustion amount of the burner 2 can be computed based on such an amount of heating in the heat exchanger 3 as can be obtained from the amount of water flow through the heat exchanger 3, the temperature of water feed to the heat exchanger 3, and the temperature of water discharge from the heat exchanger 3.
The process then proceeds to STEP 3, where a discrimination is made as to whether the supply/exhaust resistances as detected in the inspection operation are within a predetermined reference range or not. If abnormalities of the air supply tube 6 and the exhaust pipe 7 such as clogging, disconnection and the like are present in the air supply tube 6 and the exhaust pipe 7, the detected supply/exhaust resistances will be outside the reference value. In such a case, the process proceeds to STEP 4, where displaying is made by using the remote control unit 9 a to show that the air supply tube 6 and the exhaust pipe 7 are abnormal.
On the other hand, if the detected supply/exhaust resistances are within the reference range, the process proceeds to STEP 5, where searching is made to obtain a maximum set combustion amount YQmax corresponding to the supply/exhaust resistances as detected in the inspection operation based on the change characteristics held in memory. Then, the process proceeds to STEP 6, where a discrimination is made as to whether a deviation between the obtained maximum set combustion amount YQmax and the actually measured maximum combustion amount Qmax that is the combustion amount of the burner 2 as detected in the inspection operation, is within the predetermined allowable range (e.g., within ±5% of the maximum set combustion amount) or not. Then, if the deviation between the maximum set combustion amount YQmax and the actually measured maximum combustion amount Qmax is within the allowable range, the process proceeds to STEP 7, where displaying of “primary pressure normal” is made by using the remote control unit 9 a to show that the primary pressure of the fuel gas is normal.
If, on the other hand, the deviation between the maximum set combustion amount YQmax and the actually measured maximum combustion amount Qmax is outside the allowable range, the process proceeds to STEP 8, where a secondary inspection operation is performed to obtain the saturated value Nsat. In concrete, the secondary inspection operation is performed, while operating the combustion apparatus with the rotational speed of the combustion fan 5 being lowered to a value Nlow which is lower by a predetermined rate (e.g., by 20%) than the upper limit value Nmax, to thereby detect the combustion amount of the burner 2. Then, the process proceeds to STEP 9, where a discrimination is made as to whether a rate of decrease (=(Qmax/Qlow)−1) of the combustion amount Qlow of the burner 2 as detected in the secondary inspection operation relative to the actually measured maximum combustion amount Qmax is above a predetermined threshold value (e.g., 4%) or not.
Then, if the rate of decrease of the combustion amount Qlow of the burner 2 as detected in the secondary inspection operation relative to the actually measured maximum combustion amount Qmax is above the predetermined threshold value, a judgment is made that the primary pressure of the fuel gas is not abnormal although it is rather insufficient. A processing is thus performed to lower the upper limit value, for control purpose, of the rotational speed of the combustion fan 5. In other words, the process proceeds to STEP 10, where computation is made of the saturated value Nsat based on the above-mentioned rate of decrease, and the upper limit value, for control purpose, of the rotational speed of the combustion fan 5 is changed to the saturated value Nsat whose upper limit value has been computed. With reference to line “b” in FIG. 3, the proportional constant of the combustion amount relative to the rotational speed of the combustion fan is defined to be k. Then, we obtain Qlow=k·Nlow, Qmax≈k·Nsat. Because the above-mentioned rate of decrease is approximately equal to (Nsat/Nlow)−1, the saturated value Nsat can be computed based on the above-mentioned rate of decrease. Thereafter, displaying is made in STEP 11 of the changed upper limit value, i.e., of the upper limit value showing the saturated value Nsat by using the remote control unit 9 a. It is to be noted here that displaying of this upper limit value may alternatively be of the rate of the rotational speed of the combustion fan 5 relative to the normal upper limit value Nmax, that is, the rate of the combustion amount to be obtained at the changed upper limit value relative to the set maximum combustion amount YQmax. Or else, the displaying of the upper limit value may be to show the combustion amount that can be obtained at the changed upper limit value.
On the other hand, in case the primary pressure of the fuel gas is largely insufficient due to clogging of the gas pipe or the like, as illustrated by line “c” in FIG. 3, the saturated value will be below, or substantially equivalent to, the rotational speed Nlow of the combustion fan 5 at the time of the secondary inspection operation. The rate of decrease will thus be as small as below the threshold value. In this case, the process proceeds to STEP 12, where displaying is made of “primary pressure abnormal” to show that the primary pressure of the fuel gas is abnormal by using the remote control unit 9 a.
According to this embodiment, in case the supply/exhaust resistances are large although the primary pressure of the fuel gas is normal, and even if the actually measured maximum combustion amount Qmax is reduced, a comparison is made between the maximum set combustion amount YQmax that corresponds to the supply/exhaust resistances as detected in the inspection operation and the actually measured maximum combustion amount Qmax. Therefore, the deviation between the two will be within the allowable range. The upper limit value of rotational speed of the combustion fan 5 will therefore not be changed in the secondary inspection operation. Accordingly, the upper limit value of rotational speed of the combustion fan 5 can be prevented from being unnecessarily lowered under the influence of the supply/exhaust resistances.
Further, by performing the displaying in STEP 4 of “air supply tube and exhaust pipe abnormal,” the displaying in STEP 7 of “primary pressure normal,” and the displaying in STEP 12 of “primary pressure abnormal,” a discrimination can be easily made by the installer of the combustion apparatus as to whether the air supply tube 6, the exhaust pipe 7 and the fuel gas supply passage 81 have problems such as clogging, disconnection and the like. Further, if there are problems, he can easily discriminate where the problems lie. Still furthermore, by making in STEP 11 the upper limit value displaying, the user can be informed of the lowering of the heating capacity even if the heating capacity is lowered as a result of changing of the upper limit value of the rotational speed of the combustion fan. In this manner, the user can be prevented from wrongly taking the phenomenon as a mechanical trouble.
A description has so far been made of the embodiment of this invention with reference to the drawings, but this invention shall not be limited to the above. For example, it is also possible in the secondary inspection operation: to gradually lower the rotational speed of the combustion fan 5 from the upper limit value Nmax; to compare the combustion amount at the rotational speed of each stage with the combustion amount at the rotational speed of one stage lower; and to obtain the saturated value Nsat based on the change in the difference between the two. However, this procedure takes time in performing the secondary inspection operation. Therefore, the above-mentioned embodiment is more advantageous, i.e., the embodiment in which the combustion apparatus is operated only once in a state in which the rotational speed of the combustion fan 5 is lowered from the above-mentioned upper limit value Nmax by a predetermined rate and subsequently the secondary inspection operation is performed.
Further, in the above-mentioned embodiment, zero governor system of gas amount regulating means 8 is employed, but proportional valve system of gas amount regulating means may also be used. In this case, the value of the electric current to be charged to the proportional valve can be the operational quantity of the gas amount regulating means. Further, the to-be-heated object that is contained in the combustion box 4 may be other than the heat exchanger 3. In the above-mentioned embodiment, both the air supply tube 6 and the exhaust pipe 7 are provided as an auxiliary tube. This invention is however similarly applicable as a method of controlling the combustion apparatus that is provided with only one of the air supply tube 6 and the exhaust pipe 7.


Explanation of Reference Marks

2 burner,

3 heat exchanger (to-be-heated object)

	4 combustion box	4a exhaust port
	5 combustion fan	6 air supply tube
	7 exhaust pipe

	8 gas amount regulating means

Claims

What is claimed is:

1. A method of controlling a combustion apparatus, the combustion apparatus comprising: a burner; a combustion box for disposing therein a to-be-heated object that is heated by combustion gas from the burner; a combustion fan for supplying combustion air to the burner; at least one of an air supply tube communicated with a suction side of the combustion fan, and an exhaust pipe communicated with an exhaust port of the combustion box; and a gas amount regulating means for regulating an amount of fuel gas supply to the burner, the method comprising:

searching in advance for change characteristics of a maximum set combustion amount due to change in flow resistance through an auxiliary tube, where the maximum set combustion amount is defined to be such a burner combustion amount as will originally be obtainable when a primary pressure of the fuel gas is normal and when an operational quantity of the gas amount regulating means is at an upper limit value at which the fuel gas supply amount becomes maximum, and where the auxiliary tube is defined to be whichever of the air supply tube and the exhaust pipe the combustion apparatus is provided with;

performing an inspection operation while operating the combustion apparatus in a state in which the operational quantity of the gas amount regulating means is kept at the upper limit value, in order to detect the flow resistance through the auxiliary tube and the burner combustion amount;

obtaining, from the change characteristics, the maximum set combustion amount that corresponds to the flow resistance, as detected in the inspection operation, through the auxiliary tube;

when a deviation between the maximum set combustion amount and the actually measured maximum combustion amount that is the burner combustion amount as detected in the inspection operation is outside a predetermined allowable range, performing a secondary inspection operation to obtain a saturated value which is such a value of the operational quantity of the gas amount regulating means as the burner combustion amount will cease to increase even if the operational quantity of the gas amount regulating means is increased; and

changing the upper limit value of the operational quantity of the gas amount regulating means to the obtained saturated value.

2. The method of controlling a combustion apparatus according to claim 1, wherein the inspection operation is performed at a time of trial operation after having placed in position the combustion apparatus, the method further comprising:

when the flow resistance through the auxiliary tube as detected in the inspection operation is outside a predetermined reference range, displaying “auxiliary tube abnormal” which means that the auxiliary tube is abnormal; and

when a deviation between the maximum set combustion amount that corresponds to the flow resistance through the auxiliary tube as detected in the inspection operation and the actually measured maximum combustion amount is within the allowable range, displaying “primary pressure normal” which means that the primary pressure of the fuel gas is normal.

3. The method of controlling a combustion apparatus according to claim 1, wherein the secondary inspection operation is performed by detecting the burner combustion amount while operating the combustion apparatus in a state in which the operational quantity of the gas amount regulating means is lowered by a predetermined rate from the upper limit value, the method further comprising computing the saturated value based on the rate of decrease of the burner combustion amount as detected in the secondary inspection operation relative to the actually measured maximum combustion amount.

4. The method of controlling a combustion apparatus according to claim 3, wherein, when the rate of decrease of the burner combustion amount as detected in the secondary inspection operation relative to the actually measured maximum combustion amount is below a predetermined threshold value, displaying “primary pressure abnormal” is made showing that the primary pressure of the fuel gas is abnormal.

5. The method of controlling a combustion apparatus according to claim 1, further comprising:

when the upper limit value of the operational quantity of the gas amount regulating means is changed to the saturated value, displaying the upper limit value which shows the changed upper limit value.