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26
SERVICING
PROCEDURES
General Location of Controls
Fast-
Response
Temperature
Sensor
2-Stage Controller
Relay
Ignition Module
(Auto Ignition Only)
Fig. 25: Control Box Component Locations
Models 135 & 180
CIRCULATOR
VENT SENSOR
BYPASS VALVE
(MODELS 135 & 180 ONLY)
BYPASS LINE
TEMPERATURE
A
ND PRESSURE GAUGE
2-STAGED CONTROLLER
(MODEL 90 ONLY)
PRESSURE
RELIEF VALVE
RELAY
ADJUSTABLE
HIGH LIMIT
FIELD WIRING
COMPARTMENT
FAST RESPONSE
TEMPERATURE SENSOR
IGNITION MODULE
(AUTO IGNITION ONLY)
TRANSFORMER
ROLL-OUT SENSOR
GAS VALVE
Fig. 26: Component Locations
SEQUENCE OF
OPERATION
Intermittent Ignition Device
(IID)
Boilers equipped with the IID system will automatical-
ly light the pilot burner first and then the main burner,
each time there is a call for heat from the room ther-
mostat. Whenever the room thermostat is calling for
heat, the circulator supplied with the boiler will be
energized and should be running.
The ignition control module will also be energized to
initiate the pilot ignition by opening the first main valve
(pilot). At the same time, the electronic spark genera-
tor in the module produces a high-voltage spark output
that lights the pilot burner. If the pilot burner does not
light, the module will not energize the second main
valve and the burners will not light.
Ignition spark continues only until the timed trial for
ignition period ends. Then, the module goes into safe-
ty shutdown or lockout. Lockout de-energizes the first
main valve operator and closes the first main (pilot)
valve in the gas control, stopping pilot gas flow. The
ignition control system must be reset by setting the
thermostat below room temperature for one minute or
by turning off power to the module for one minute.
When the pilot flame is established, flame rectification
circuit is completed between the sensor and burner
ground. The flame sensing circuit in the module
detects the flame current, shuts off the spark genera-
tor and energizes the second main valve operator
which opens the second main valve. This allows gas to
flow to the burners where it is ignited by the pilot burn-
er flame.
When the thermostat is satisfied, the valve operators
are de-energized shutting off the pilot and main burn-
ers, and also the circulator.