PRESSURE REGULATION
The pressure regulator supplied with the water heater is adjusted to operate on the gas specified on the rating plate and:
•in Canada, is factory preset to deliver gas at the high altitude setting listed on the rating plate and as shown below.
•in the U.S.A., is factory preset to deliver gas at the standard altitude setting listed on the rating plate and as shown below.
The pressure setting of the gas pressure regulator should be checked at installation to assure that the setting is correct for the gas being used and the altitude at which the appliance is installed. See rating plate on the unit, Table 1, below, for proper setting.
In Canada, for a heater being installed at standard altitude
REGULATOR
SUPPLY TEST
PRESSURE TAP T
ADJUSTABLE
PRESSURE REGULATOR
Figure 10
The gas pressures specified below refer to flow pressure taken at the pressure tap in the gas inlet pipe just above the pressure regulator, (see figure 10) while the heater is operating at full input.
Gas pressures read at burner test point D (see fig. 7) page 13.
Table 1.
Appliance Regulator Pressure Setting
Model | Type of Gas | Pressure tap | Altitude | ||
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kPa | Inches, W.C. | ||||
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| natural | 1.41 | 5.38 | standard | |
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propane | 2.61 | 9.9 | |||
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natural | 1.14 | 4.4 | high* | ||
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| propane | 2.09 | 7.9 | ||
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*Note: The high altitude ratings listed are Canadian Gas Association high altitude ratings for the appliances and are only valid in Canada. In the U.S.A. the National Fuel Gas Code, ANSI 1- 1988, recommends for high altitude installations, above 2,000 feet, that the input rate be reduced 4% for each 1,000 feet above sea level.
Your appliance dealer and/or your local gas supplier should be consulted in regard to any high altitude installation. If field adjustment is required it should be performed by a qualified serviceman experienced in such work.
TEMPERATURE REGULATION
The BOSCH
Temperature Adjustment Knob
Decreases temperature | Increases temperature |
and increases flow | and decreases flow |
Figure 11 - Principles of Operation
With the water flow selector turned to its right hand stop position (50°C rise setting) and with an inlet water temperature of 10°C (50°F) the outlet water temperature will be maintained at approximately 60°C (140°F) in the water flow rate range of approximately 2 litres/min. (0.5 U.S. gals./min.) to 9.5 litres/min. (2.5 U.S. gals./min.).
The minimum flow rate for operation, the “Threshold Flow Rate” referred to in the lighting instructions is 2 litres/min (0.5 U.S. gals./min.). If the water flow rate is below this level the main burner will not fire. If the flow rate exceeds 9.5 litres/min (2.5 U.S. gals./min.) the temperature rise aross the heater will decrease in proportion to the rate above this temperature.
HIGH TEMPERATURE LIMIT SWITCH
The BOSCH series instantaneous gas water heaters are equipped with a high temperature limit switch with a set point of approximately 90°C (195°F). If the water temperature at the sensing points exceeds the set point the switch will open, interrupting the safety circuit and stopping gas flow to the pilot and main burner.
Outage as the result of high limit operation indicates that the heater is not functioning properly. The heater should be checked by a qualified serviceman and the reason for the malfunction is corrected.
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