Operating instructions

38
1. Standing Pilot (24) Sequence of Operation
a. Normal Operation
i. Thermostat or operating control calls for
heat. Vent Damper (if used) opens.
ii. Gas valves are energized allowing main gas
flow and ignition of main burners.
iii. Call or heat ends. Gas valves are de-
energized, extinguishing main flame. Vent
Damper (if used) closes.
b. Safety Shutdown
i. Limit: Automatically interrupts main burner
operation when water temperature exceeds
set point. Maximum allowable temperature is
250°F. Circulator continues to operate with
call for heat, Vent Damper (if used) closes.
Normal operation resumes when water
temperature falls below set point.
ii. Blocked Vent Switch: Automatically
interrupts main burner operation when
excessive flue gas spillage occurs. Circulator
continues to operate and Vent Damper (if
used) remains open with call for heat. If
blocked vent switch is activated do not
attempt to place boiler in operation. Correct
cause of spillage and reset blocked vent
switch.
iii. Flame Roll-out Switch: Automatically
interrupts main burner operation when
flames or excessive heat are present in
vestibule. Circulator continues to operate
and Vent Damper (if used) remains open with
call for heat. Control is single use device. If
flame roll-out switch is activated, do not
attempt to place boiler in operation. Correct
cause of spillage and replace flame roll-out
switch.
iv. Thermocouple: Senses pilot flame and
causes gas valves to turn off main burner
and pilot burner gas flow should pilot burner
flame extinguish. Circulator continues to
operate and Vent Damper (if used) remains
open with call for heat.
Table 10: Sequence of Operation and Wiring Diagrams
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