Hydronic Heating Boilers and Domestic Water Heaters
Electronic Temperature Controller
(Operator)
A
Ignition Module
(Controlled by Electronic Temperature Controller)
One ignition module is provided on the unit. Upon sensing the 24VAC delivered to it by the electronic temperature controller, the ignition module checks for a shorted pressure switch and then, provided the air switch isn't shorted, supplies 120VAC to its blower output relay and waits for a pressure switch signal.
Two Speed Blower (Controlled by Ignition Module and Relay Board)
A single
Pressure Switch (Activated by Blower Turning On)
One pressure switch is provided to monitor the blower On/Off operation. Upon a call for heat, 24VAC is delivered to the pressure switch. If the blower generates adequate air pressure, the pressure switch closes to deliver 24VAC to the ignition module pressure switch monitoring input terminal.
Prepurge (Ignition Module Function)
Once the ignition module sees a 24VAC input from the pressure switch, it runs the blower for approximately 15 seconds in order to purge the combustion chamber of any unburned fuel/air mixture.
Trial for Ignition (Ignition Module Function)
Once the ignition module has completed its prepurge period, it turns on the hot surface igniter. Once the hot surface igniter's current draw reaches a proper level, the ignition module begins a trial for ignition period of approximately 25 seconds to allow time for the igniter to reach the ignition temperature necessary to ignite the fuel/air mixture.
Igniter (Controlled by Ignition Module)
One igniter is provided in order to ignite the fuel/air mixture and its on/off operation is controlled by the ignition module.
Relay Board (Controlled by Electronic Temperature Controller and Ignition Module)
A small relay board is provided on the 985,000 - 2,065,000 Btu/hr models to switch the blower from low to high speed and to deliver power from the low fire stage (Stage 1) to the high fire stage (Stage 2) depending upon the electronic thermostat's settings.
Ignition (Ignition Module Function)
Once the trial for ignition period has been completed, the ignition module sends 24VAC to the gas valves on the low fire stage (Stage 1). Gas valves should open and allow gas to flow to the burners in Stage 1 being energized. The fuel/air mixture should ignite from the hot surface igniter. Once this voltage has been sent to the valves, the hot surface igniter is turned off. The ignition module then monitors the status of the flame and will either allow ignition to continue or shut down the gas valves should flame not be proven and proceed to a Flame Failure condition. If flame was proven briefly during the ignition period, the module may not proceed to Flame Failure, but rather
Heat Transfer Process (Gas Valves, Burner,
and Heat Exchanger)
Once flame has been proven, the ignition module will hold the gas valves open as long as there is proof of flame and a call for heat is present. If the low fire stage cannot provide enough heat to raise the system temperature, the electronic temperature controller turns on the high fire stage. The high fire stage will operate until the system water temperature shows a gain that can be handled by low fire operation. The high fire stage shuts off at this point. When the
When 24VAC is removed from the ignition module's thermostat input, the module turns off the gas valves and maintains the blower for approximately 25 seconds in order to allow the combustion chamber to be purged of all combustion
Pump Delay (Electronic Thermostat Function)
When the electronic thermostat removes 24VAC from the ignition module, it continues to hold the pump relay on for 30 seconds in order to get the remaining heat out of the combustion chamber. The pump then turns off to prevent the heat in the water from going back into the combustion chamber and up the flue.
Idle (Electronic Thermostat Function)
After completion of the
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