Burnham Series 2B - Manual (Page 15)

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Figure 13: Wiring Diagram,  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 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. 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
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.