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Figure 14: Wiring Diagram, 24 Volt Standing Pilot with Continuous or Gravity Circulation
SEQUENCE OF OPERATION
NORMAL OPERATION
1. When the thermostat call for heat, the vent damper
will open (see paragraphs 17A through 17D). The gas
valve is energized allowing main gas to flow and
operation of the main burners.
2. Where condensation of flue gas is encountered in
boiler flues a reverse acting circulator control should
be installed to stop the circulator before the boiler
water temperature drops to that which flue gas
condensation may occur.
3. After the thermostat is satisfied the main valve will
close and main burner flames will be extinguished.
The vent damper will close (see paragraph 17E). If the
boiler is so equipped, circulator will continue to run.
SAFETY SHUTDOWN
1. High Limit Switch
In the event excessive boiler water temperature is
developed the high limit switch will open interrupting
power to the gas valve. The main burners will be
extinguished immediately. Normal operation will be
resumed when the boiler water temperature drops to a
point where the high limit switch closes.
2. Blocked Vent Switch
In the event excessive blockage in the vent system is
developed the blocked vent switch will open interrupt-
ing power to the gas valve. The main burners will be
extinguished immediately and the vent damper will
remain open until the thermostat is turned off. The
source of blockage must be corrected by trained and
skilled personnel from a qualified service agency
before resetting switch.
3. Flame Rollout Switch
In the event excessive blockage in the boiler section
flue passageways is developed the flame rollout switch
will open interrupting power to the gas valve. The
main burners will be extinguished immediately and
the vent damper will remain open until the thermostat
is turned off. If the flame rollout switch is activated do
not attempt to place the boiler in operation. The source
of the blockage must be corrected and the flame
rollout switch replaced by trained and skilled person-
nel from a qualified service agency.
4. Pilot
The thermocouple proves pilot flame and in the
absence of such within 45-90 seconds causes the
combination gas valve, which is equipped with a
100% shut-off provision, to be de-energized, thus,
preventing main gas or pilot gas flow.