Tank Sensor Or Mechanical Control; System/Pipe Sensor; Optional High Gas Pressure Switch; Optional Low Gas Pressure Switch - Heat Transfer MODCON VWH 300 LP Installation & Maintenance

PART 8: FIELD WIRING
G TANK SENSOR OR MECHANICAL
CONTROL
Connect the tank sensor or mechanical controls
to the TANK SENSOR terminals of the low volt-
age terminal strip as shown in Fig. 8-1. The con-
trol will automatically determine which type of
sensor is connected and will operate according-
ly. Caution should be used to ensure that neither
of these terminals becomes connected to
ground.
H. SYSTEM / PIPE SENSOR
The System/Pipe sensor can be used to control
the temperature of the storage tank when a Tank
Sensor or Mechanical control cannot be mount-
ed. The System/Pipe Sensor would be wired
into the terminals of the low voltage terminal
strip as shown on figure 8-1. It is important to
note that when a System/Pipe Sensor is used,
the circulating pump must be wired to operate
continuously, otherwise the boiler will short
cycle.
The System/Pipe sensor can also be used in a
Cascade System when the sensor is placed on
the supply line of multiple boilers that feed the
storage tank. This will control the temperature
and modulate the firing rate of the connected
boilers. The System/Pipe Sensor would then be
wired into the Master Boiler terminals on the low
voltage strip as shown on figure 8-3.
I. OPTIONAL HIGH GAS PRESSURE
SWITCH
1. If an optional high gas pressure switch is
47
GAS-FIRED HOT WATER SUPPLY BOILER
(CONTINUED)
used, it should be installed on the outlet side
of the gas valve. This is normally closed and
will open if the pressure goes above 1.5" w.c.
on the outlet side.
2. Locate the two pigtails hanging from the
electrical box inside of the boiler cabinet.
Remove and discard the jumper plug from
one of the unused pigtails.
3. Connect the high gas pressure switch to the
pigtail that you removed the jumper plug
from.
J. OPTIONAL LOW GAS PRESSURE
SWITCH
1. If an optional low gas pressure switch is
used, it should be installed on the inlet side
of the gas valve. This is normally closed and
will open if the pressure goes below 1" w.c.
on the inlet side.
2. Locate the two pigtails hanging from the
electrical box inside of the boiler cabinet.
Remove and discard the jumper plug from
one of the unused pigtails.
3. Connect the low gas pressure switch to the
pigtail that you removed the jumper plug from.
K. FLOW SWITCH
The MODCON VWH boiler requires the use of a
flow switch. The flow switch kit 7350P-605 or
7350P-606 is part of the VWH conversion
process and comes packaged with detailed
installation instructions which should be read
and followed to ensure a functional system
Boiler Manual