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13
SEQUENCE OF OPERATION
Normal Operation
1. When the thermostat call for heat, the vent damper
will open (see paragraphs 17A through 17D). The
circulator is started through a relay and at the same
time the gas valve is energized allowing main gas
ow and ignition of main burners.
2. Where condensation of ue gas is encountered in
boiler ues a reverse acting circulator control should
be installed to stop the circulator before the boiler
water temperature drops to that which ue gas
condensation may occur.
3. After the thermostat is satised the main valve will
close and main burner ames will be extinguished.
The vent damper will close (see paragraph 17E).
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, and the
vent damper will close at the same time, but the
circulator will continue to operated. Normal
operation will be resumed when the boiler water
temperature drops to a point where the high limit
switch closes.
Figure 11: Wiring Diagram, 24 Volt Standing Pilot and Intermittent Circulation
2. Blocked Vent Switch
In the event excessive blockage in the vent system is
developed the blocked vent switch will open
interrupting power to the gas valve. The main
burners will be extinguished immediately, the
circulator will continue to operate, 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
qualied service agency before resetting switch.
3. Flame Rollout Switch
In the event excessive blockage in the boiler section
ue passageways is developed the ame rollout
switch will open interrupting power to the gas valve.
The main burners will be extinguished immediately,
the circulator will continue to operate and the vent
damper will remain open until the thermostat is
turned off. If the ame rollout switch is activated do
not attempt to place the boiler in operation. The
source of blockage must be corrected and the ame
rollout switch replaced by trained and skilled
personnel from a qualied service agency.
4. Pilot
The thermocouple proves pilot ame 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 ow.