How It Works - Weil-McLain CGi 4 Series Manual

CGi
SERIES 4 — GAS-FIRED WATER BOILER —

How it works . . .

Control module
The control module responds to signals from the room thermostat, air pressure switch and boiler limit circuit to
operate the boiler circulator, pilot burner, gas valve and inducer. When room thermostat calls for heat, the control
module starts the system circulator and inducer.
The control module runs the inducer long enough to purge the boiler flue passages, then opens the pilot valve
and activates pilot ignition spark.
The control module allows up to 15 seconds to establish pilot flame. If flame is not sensed within 15 seconds,
the control module will turn off the gas valve, flash the Flame light, and then enter a 15-second postpurge. The
control module will then start a new cycle. This will continue indefinitely until pilot flame is established or power
is interrupted. Once pilot flame is proven, the control module opens the gas valve to allow main burner flame.
When the room thermostat is satisfied, the control module turns off the gas valve, operates the inducer for a
15-second postpurge and waits for the next heat call.
The control module indicator lights show normal sequence when the lights are on steady. When a problem occurs,
the control module flashes combinations of lights to indicate the most likely reason for the problem (see page 49).
Transformer
The control transformer reduces line voltage to 24 volts for the gas valve and limit circuit.
Inducer
The inducer pulls flue gases through the boiler, causing air to be pulled in through the boiler air openings. The
inducer pushes the flue gases through the vent pipe as well.
Air pressure switch
The air pressure switch signals the control module, telling the control module whether the inducer is working
correctly or the vent is blocked.
Water temperature/LWCO sensor
The water temperature/LWCO sensor provides a signal to the control module to turn off the gas valve if the tem-
perature in the boiler goes above its setting or if a low water condition is sensed. (The circulator will continue to
run as long as there is a call for heat.)
Boiler circulator
The boiler circulator circulates water through the external (system) piping. The circulator is shipped loose, and can
be mounted on either the boiler supply or return piping. The factory-installed circulator wiring harness provides
ample length for either location.
not operated for 30 days, the control module will power the circulator for 30 seconds, then turn off.
Other boiler components:
a supply to system
b return from system
c stainless steel burners
d flue outlet
e gas valve
2
Boiler Manual
— The control module provides a pump exercising routine. If the boiler is
NOTE
f
pressure/temperature gauge
g relief valve
h air vent connection
i
flame rollout thermal fuse ele-
ment (TFE)
j
burner shield
k pilot burner and bracket
l
gas manifold
m cast iron boiler sections
n flue collector
o junction box
Part Number 550-142-302/0124