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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 flow
and ignition of 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).
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 interrupt-
ing 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 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, the
circulator will continue to operate 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 blockage must be corrected and the flame rollout
switch replaced by trained and skilled personnel 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.