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4) Once the vent damper is fully open, an end switch inside the damper will make, energizing pin #3 (red) at the damper. This pin is connected through the damper harness to terminal “B1” on the L8148E. At this point in the operating sequence, 24 volts is present across “B1” and “B2”. 5) Under normal conditions, the flame roll-out switch and blocked vent switch are made. Voltage will therefore immediately appear across the combination gas control (“gas valve”) terminals “TH” and “TR”. 6) When the boiler is first placed into operation, the pilot must be lit. The pilot heats a thermocouple which generates a small amount of electricity sufficient to hold open the safety shut-off valve in the combination gas control. The circuit connecting the thermocouple and the safety shut-off valve is self contained and completely independent of all other wiring on the boiler. This safety shut-off valve is upstream of the 24 volt valves in the gas control which open in response to a call for heat. If the pilot is not lit, the safety shut-off valve will remain closed and gas will not reach the 24 volt valves. 7) Assuming that the pilot is established and proven by the thermocouple, the application of 24 volts across the combination gas valve terminals energizes the redundant 24 volt solenoid valves in the combination gas control, resulting in gas flow through the control and burner operation. 19 Sequence of Operation, Intermittent Ignition Sequence of Operation, Intermittent Ignition 4) Once the vent damper is fully open, an end switch inside the damper will make, energizing pin #3 (red) at the damper. This pin is connected through the damper harness to terminal “B1” on the L8148E. At this point in the operating sequence, 24 volts is present across “B1” and “B2”. 5) Under normal conditions, the flame roll-out switch and blocked vent switch are made. Voltage will therefore immediately appear across the “24V” and “24V (GND)” terminals on the ignition module. 6) Upon application of voltage across the “24V” and “24V (GND)” terminals, the ignition module will start an ignition spark at the pilot and apply 24 volts across the pilot valve (terminals “PV” and “MV/PV”). 7) Once the pilot is established, the pilot flame will act as a diode, converting the AC current at the electrode to a half wave DC current at the pilot’s ground strap. This DC current flows through the boiler to the “GND (BURNER)” connection on the ignition module. For the ignition module to recognize that a pilot flame is present, the DC current flowing into this terminal must be in excess of approximately 1.0 uA. 8) Once the ignition module detects the presence of a pilot flame, voltage is applied across the main valve (terminals “MV” and “MV/PV”), opening the valve and establishing main flame. 9) The way in which the ignition module handles failure to establish pilot or the loss of an already established pilot depends upon the exact ignition module supplied with the boiler. For more information on module operation, consult the ignition module instructions supplied with the boiler or the local Crown representative. Safety Control Operation - Standing Pilot and Intermittent Ignition High Limit - Interrupts main burner operation when the supply water temperature exceeds set point. Maximum allowable temperature is 250°F. If the high limit opens, the vent damper will close if the damper switch is in the “automatic” position. The circulator will continue to operate as long as there is a call for heat, regardless of the status of the high limit. Burner operation automatically resumes when the supply water temperature falls below set point. Blocked Vent (“Spill”) Switch - Automatically interrupts main burner operation in the event that flue gas spills from the draft diverter opening. This switch is equipped with a reset button which must be pressed to restore normal burner operation. An open blocked vent switch is indicative of a problem with the vent system. If the blocked vent switch opens, the cause of the venting problem must be found and corrected by a qualified gas service technician before the blocked vent switch is reset. Flame Roll-out Switch - Automatically interrupts boiler operation when flames or excessive heat are present in vestibule. The flame roll-out switch is a single use device which must be replaced by a identical switch in order to restore normal operation. An open flame roll-out switch is usually indicative of a plugged heat exchanger. The cause of the flame roll-out must be found and corrected by a qualified gas service technician, and the switch replaced with an identical one, before the boiler is returned to operation. 20 X Start-up and Checkout NOTE SAFE LIGHTING AND OTHER PERFORMANCE CRITERIA WERE MET WITH THE GAS MANIFOLD AND CONTROL ASSEMBLY PROVIDED ON THE BOILER WHEN THE BOILER UNDERWENT THE TESTS SPECIFIED IN Z21.13. Use the following procedure for initial start-up of the boiler: 1) Make sure that the boiler and system are filled with water...

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