Install Instructions

67
9 Glossary
Once the ignition module sees a 24VAC input from the
pressure switch, it runs the blower 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 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.
Hi-Lo Fire Relay
The relay serves as means to switch from low fire to high
fire. On Models 987 - 2067, in addition to switching
between high fire to low fire, the relay also changes the fan
speed from high for high fire to low for low fire.
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 post-purge and then
go into another trial for ignition.
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 low-
fire stage alone produces more heat than is required, the
electronic temperature controller turns off the call for heat.
Post-Purge
(Ignition Module Function)
When 24VAC is removed from the ignition module’s thermostat
input, the module turns off the gas valves and maintains the
blower in order to allow the combustion chamber to be purged
of all combustion by-products.
Pump Delay
(Electronic Thermostat Function)
When the electronic thermostat removes 24VAC from the
ignition module, it continues to hold the pump relay on 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 post-purge cycle, the unit will go into
an idle state whereby the electronic thermostat continuously
monitors the water temperature until the water temperature
drops to levels that require additional heat.
Installation & Service Manual