How It Works - Weil-McLain CGa 2 Series Manual

CGa Series 2 Gas-Fired Water Boiler — Boiler Manual

How it works . . .

①
Control module
The control module responds to signals from the room thermostat and boiler limit circuit to operate the boiler
circulator, pilot burner, gas valve and vent damper. When room thermostat calls for heat, the control module starts
the system circulator and activates the vent damper (causing it to drive open).
When the vent damper has opened completely, the control module opens the pilot valve and activates pilot
ignition spark.
For natural gas, 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 immediately 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 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, wait 1 minute, then start a new
cycle. If flame is still not sensed after the second trial, two more attempts are made with 5 minute and 60 minute
wait periods in between. If flame 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 flame.
When the room thermostat is satisfied, the control module turns off the gas valve and deactivates the vent damper
(causing it to close).
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
for details.
②
Transformer
The control transformer reduces line voltage to 24 volts for the gas valve and limit circuit.
③
Draft hood
The draft hood provides a minimum draft for the boiler, assuring adequate air for combustion if installed in
accordance with manual and not modified in any way.
④
Spill switch
The spill switch will shut down the boiler (requiring manual reset of the switch reset button) if the vent system
becomes blocked.
⑤
Water temperature sensor
The water temperature 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.)
⑥
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. 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 turn off.
⑦
Vent damper
The vent damper closes during off cycles to reduce heat loss from the house up the vent.
Other boiler components:
a supply to system
b return from system
c flue outlet
d burner manifold
e gas valve
2
f pressure/temperature gauge
g relief valve
h air vent connection
i flame rollout switch
j
burner orifice
k pilot burner, typical
l stainless steel burners
m cast iron boiler sections
n flue collector
o junction box
Part Number 550-142-900/1016