12
LOW GAS PRESSURE SWITCH
(SEE FIGURE 12)
The Low Gas Switch (LGS) is a single-pole, normally open pressure switch
that will close its contacts when a rising pressure of 5.0 in. (1.25Kpa) W.C.
is encountered. The contacts will open when the pressure falls below the
fixed set point of 4.8"WC (1.18Kpa) for natural gas models and 8.5"WC
(2.08Kpa) for propane models. The LGS monitors the gas supply pressure
to the heater. If the gas supply falls below 5.0 in. (1.25Kpa) W.C., the main
burner is extinguished (if heater is running) or the heater will not start up.
ON/OFF SWITCH
The ON/OFF Switch is a single-pole, single-throw rocker switch. This switch
provides 120V from the line source to the heater.
CAUTION
THE WATER HEATER IS POLARITY SENSITIVE. BEFORE APPLYING
ELECTRICITY TO THIS HEATER BE CERTAIN THAT SUPPLY NEUTRAL
WIRE TO GROUND CHECK INDICATES ZERO VOLTAGE.
HOT SURFACE IGNITER
The Hot Surface Igniter is a device that ignites the main burner by high
temperature (>1800°F or >982°C). When 120VAC is applied to the igniter,
sufficient heat is generated to ignite the main burner. Although improvements
have been made to strengthen the igniter, it is still fragile and care must be
taken when handling the igniter to prevent breakage.
GAS PIPING
Contact your local gas service company to ensure that adequate gas service
is available and to review applicable installation codes for your area.
Size the main gas line in accordance with Table 3. The figures shown are
for straight lengths of pipe at 0.5" (125Pa) W.C. pressure drop, which is
considered normal for low pressure systems Note that fittings such as elbows
and tees will add to the pipe pressure drop.
CAUTION
DO NOT USE FLEXIBLE GAS PIPING.
TABLE 3. MAXIMUM CAPACITY OF PIPE IN CUBIC FEET
OF GAS PER HOUR
(Based upon a Pressure Drop of 0.5") Water Column and 0.6 Specific
Gravity Gas and max. gas pressure of 0.5 psig)
CONTROLS AND SWITCHES
All models are provided with four pressure switches. These switches are
essential to the safe and proper operation of the unit. All switches are wired
in series. The controller is set up to shut the unit down whenever there is a
failure of any of the switches. It is important to understand the purpose of
each switch.
FIGURE 12.
BLOWER PROVER SWITCH
(SEE FIGURE 12)
The Blower Prover Switch is provided on the heater to verify that the fan
is operating. It is a positive pressure switch whose electrical contacts are
normally open. When the fan increases the pressure in the burner, the
pressure switch will allow the electrical contacts to close. The pressure switch
is connected to the burner tap by a piece of tygon tubing. This tubing must
be connected in order for the switch to change the electrical contacts. The
controller requires that the electrical contacts on this air flow switch be open
before it will allow the blower to come on.
BLOCKED OUTLET PROVER SWITCH
(SEE FIGURE 12)
The Blocked Outlet Prover Switch is set up to shut the unit off when a build-up
of positive pressure in the exhaust vent pipe occurs. This switch is a positive
pressure switch that requires an increase in pressure to change the electrical
contacts from normally closed to open. When this switch prevents the unit
from igniting, most likely the exhaust is blocked by some means Check to
see if the condensate is allowed to flow freely from the exhaust elbow and
for obstructions in the exhaust venting and exhaust vent terminal. Also verify
that there is no more than fifty equivalent feet (15.2 m) of three inch PVC
vent pipe on the exhaust.
BLOCKED INLET PROVER SWITCH
(SEE FIGURE 12)
The Blocked Inlet Prover Switch is set up to shut the unit off when a build-up
of negative pressure in the intake vent pipe occurs. This switch is a negative
pressure switch that requires an increase in negative pressure to change the
electrical contacts from normally closed to open. The switch is connected
to the pressure tap on the PVC flange connected to the inlet of the blower.
When this switch prevents the unit from igniting, most likely the intake is
blocked by some means. Check to see if there is no more than fifty equivalent
feet (15.2 m) of three inch PVC vent pipe on the intake. Also verify that the
intake and intake vent terminal is free of obstructions that may prevent air
from entering the unit.
LENGTH
NORMAL IRON PIPE SIZES (INCHES)
IN
INPUT IN THOUSANDS BTU/HR
FEET
1/2" 3/4" 1" 1 1/4" 1 1/2" 2" 2 1/2"
3"
4"
10
175 360 680 1400 2100 3960 6300 11000 23000
20
120 250 485 950 1460 2750 4360 7700 15800
30
97 200 375 770
1180 2200 3520 6250 12800
40
82 170 320 660
990 1900 3000 5300 10900
50
73 151 285 580
900 1680 2650 4750 9700
60
66 138 260 530
810 1520 2400 4300 8800
70
61 125 240 490
750 1400 2250 3900 8100
80
57 118 220 460
690 1300 2050 3700 7500
90
53 110 205 430
650 1220 1950 3450 7200
100
50 103 195 400
620 1150 1850 3250 6700
125
44
93 175 360
550 1020 1650 2950 6000
150
40
84 160 325
500 950 1500 2650 5500
175
37
77 145 300
460 850 1370 2450 5000
200
35
72 135 280
430 800 1280 2280 4600
LENGTH
NORMAL IRON PIPE SIZES (INCHES)
IN
INPUT IN KW
METERS 1/2" 3/4" 1" 1 1/4" 1 1/2" 2" 2 1/2"
3"
4"
3.0
51 105 199 410
615 1160 1845 3221 6735
6.1
35
73 142 278
428 805 1277 2255 4626
9.1
28
59 110 225
346 644 1031 1830 3748
12.2
24
50
94
193
290 556 878 1552 3192
15.2
21
44
83
170
264 492 776 1391 2840
18.3
19
40
76
155
237 445 703 1259 2577
21.3
18
37
70
143
220 410 659
1142 2372
24.4
17
35
64
135
202 381 600 1083 2196
27.4
16
32
60
126
190 357 571 1010 2108
30.5
15
30
57
117
182 337 542
952 1962
38.1
13
27
51
105
161 299 483
864 1757
45.7
12
25
47
95
146 278 439
776 1610
53.3
11
23
42
88
135 249 401
717 1464
61.0
10
21
40
82
126 234 375
688 1347
