How It Works - Weil-McLain CGi Series 3 Installation And Maintenance Manual

CG i
GAS-FIRED wATER BOILER- sERIEs a -
Boiler Manual
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,!ilot burner, gas valve and inducer. When room thermostat calls for heat, the control module starts the
system circulator an inducer.
The control module nms the inducer long enough to purge the boiler flue passages, then opens the pilot valve and activates
pilot ignition spark.
For natural gas, the control module allows up to IS seconds to establish pilot flame. If flame is not sensed within IS seconds,
the control module will turn off the gas valve, flash the Flame light, and then enter a IS-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.
For propane gas, the control module allows up to IS seconds to establish pilot flame. If flame is not sensed within IS seconds,
the control module will tum
off the gas valve,
flash the Flante light, wait I minute, then start a new cycle. If flame is still not
sensed after the second trial, two more attempts are made with S minute wait periods in between. If flante is not sensed after
4 tries, control will lockout and flash all lights. Control must be manually reset
to
place back into service. Once pilot flame
is proven, the control module opens the gas valve to allow main burner flante.
When the room thermostat is satisfied, the control module turns off the gas valve, operates the inducer for a IS-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).
@
Transfonner
The control transformer reduces line voltage to
24
volts for the gas valve and limit circuit.
@
Induce r
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 sw it ch
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 limit sensor
The water temperature limit sensor provides a signal to the control module to turn off the gas valve if the temperature in the
boiler goes above its setting. (The circulator will continue to run as long as there is a call for heat.)
@
Boller 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. NOTE - The control module provides a pump exercising routine. If the boiler is not operated for
30
days, the
control module will power the circulator for
30
seconds, then tum off.
Timer relay - CGI 4 Only
The timer relays delays high fire for
60
seconds.
Other boile r components:
2
a supply to system
b
return from system
c
stainless steel burners
d flue outlet
e gas valve
f
pressure/temperature gauge
g
relief valve
h
air vent connection
i
flame rollout thermal fuse element
(TFE)
j burner shield
k pilot burner and bracket
1 gas manifold
m cast iron boiler sections
n
flue collector
o junction box
Part Number 550-142-780/0712