Pressure Regulation; High Temperature Limit Switch - Bosch WR400-1K Series Installation Operation & Maintenance

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 pressure 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 of the unit, or Table
1, below, for proper setting.
In Canada, for a heater being installed at standard altitude
(0- 2,000 ft. above sea level), the manifold pressure should
be reset at installation to value shown on the rating plate, or
Table 1, below, for standard altitude.
Figure 9
The gas pressure specified below refer to flow pressure taken
at the pressure tap in the gas inlet pipe (just above the
pressure regulator), see figure 9 while the heater is operating
at full input.
Type Pressure tap
of gas kPa
Natural 1.41
Propane 2.61
Natural 1.14
Propane 2.09
* Note: The high altitude ratings listed are Canadien 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 Z223. 1 /NFPA 54,
recommends for high altitude installations, above
2,000 feet, that the input rate be reduced 4% for
each 1,000 feet above sea level.
8
PRESSURE TAP
PRESSURE
REGULATOR
Altitude
inches W.C.
5.7 standard
10.5 (0 - 2,000 ft)
4.6 high*
8.4 (2,000 - 4,500 ft)
Your appliance dealer and/or your local gas supplier should
be consulted in regard to any high altitude installation. If
filed adjustment is required it should be performed by a quali-
fied serviceman experienced in such work.
TEMPERATURE REGULATION
The BOSCH WR400-1 is equipped with a modulating gas
valve which adjusts the flow of gas to the main burner in
proportion to the water flow rate. Within its heating capac-
ity the WR400-1 attempts to maintain burner in proportion
to the water flow rate. Within its heating capacity the
WR400-1 attempts to maintain the set temperature rise
across the heater. This temperature rise can be set in range
of 25ºC –to- 50ºC (45º F – to – 90ºF), by means of the
water flow selector. See figure 10. With the gas control
button slid all the way to the right under the "ON" position
mark @ when the water flow selector is turned to the right
hand stop the water flow selector is turned to the right hand
stop the water heater is set for 50ºC (90ºF) temperature
rise; when the water flow selector is set to the left hand
stop it is set for 25ºC (45ºF) temperature rise.
Figure 10
With the water flow selector turned to its right hand stop
position (50ºC rise setting) and with an inlet water
temperature of 10ºC (50ºF) the outlet water temperature
will be maintained at approximately 60ºC (140ºF) in the water
flow rate range of approximately 2 litres/min. (0.5 U.S.gals/
min) to 8 litres /min. (2. 1 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 excess 8 litres/
min (2. 1 U.S. gals/min.) the temperature rise across the heater
will decrease in proportion to the rate above this temperature.

HIGH TEMPERATURE LIMIT SWITCH

The BOSCH WR series instantaneous gas water heaters
are equipped with a high temperature limit switch with a set
point of approximately 90ºC (194ºF). 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. To relight the pilot, follow
instructions provided on the unit.
GAS CONTROL
SLIDE
WATER FLOW
SELECTOR