How The Boiler Works; Air Pressure Switch; Water Temperature Sensor - Weil-McLain Gold GV Series 4 User's Information Manual

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How the boiler works . . .

Control module
The GOLD Control Module (GCM) responds to signals from the room thermostat, air pressure
switch, inlet water sensor and boiler limit circuit to operate the circulators, gas valve, igniter and
blower. When a room thermostat calls for heat, the GCM starts the system circulator and blower.
The GCM runs the blower long enough to purge the boiler flue passages, then turns on the igniter
and lets it warm up.
After a 15-second warmup, the GCM opens the gas valve, turns the igniter off, and checks for
flame. The flame must come on within 4 seconds or the GCM will shut down and try the full cycle
again.
When the room thermostat is satisfied, the GCM turns off the boiler components and waits for the
next heat call.
The GCM indicator lights show normal sequence when the lights are on steady. When a problem
occurs, the GCM flashes combinations of lights which indicate the most likely reason for the
problem.
Transformer
The control transformer reduces line voltage to 24 volts for the gas valve and limit circuit.
Blower
The blower pulls in air and mixes it with gas from the gas valve. The blower forces this mixture into
the burner for combustion inside the boiler chamber.

Air pressure switch

The air pressure switch signals the control module, telling the control module whether air is
moving through the blower.
Water temperature limit switch
The water temperature limit switch turns off the gas valve if the temperature in the boiler goes
above its setting. (The circulators will continue to run as long as there is a call for heat.)
System circulator
The system circulator circulates water through the external (system) piping. The flow rate of the
circulator is controlled by the GCM, depending on the temperature of the water entering the boiler
sections. Pump must remain on boiler — do not remove.
Bypass circulator
The GCM operates the bypass circulator to mix hot water from the boiler outlet with colder return
water from the system when needed to prevent condensation of flue gases in the boiler.
When the water returning to the boiler is below 140 °F, the GCM regulates the bypass circulator
and system circulator flow rates to raise the water temperature up to 140 °F before it enters the
boiler sections. By balancing these flow rates, the GCM can protect against condensation even if
return water is as low as 60 °F.
Pump must remain on boiler — do not remove.

Water temperature sensor

The water temperature sensor monitors the temperature of the water entering the boiler sections.
The sensor sends this information to the GCM, telling the GCM how much to adjust the circulator
flow rates to provide at least 140 °F entering water.
Part number 550-141-866/1202