Sequence Of Operation - Dunkirk XEB-2 Installation, Operation & Maintenance Manual

Sequence of Operation - Refer to Figure 13
1.
Thermostat calls for heat, powering the 1K relay coil
and closing contacts 1K1 and 1K2.
2.
Circulator pump is powered through terminals C1 and
C2.
3.
Induced draft blower and transformer primary are
powered through terminals B1 and B2.
4.
When blower gets up to speed and blower suction
pressure reaches pressure switch set point, pressure
switch contacts close sending 24 volts to intermittent
pilot control from transformer secondary.
5.
Pilot gas valve opens and spark initiates to light pilot
burner.
6.
When pilot flame is proven, spark drops out.
7.
Main gas valve opens and pilot burner ignites main
burners.
8.
If boiler water temperature reaches high limit set point,
high limit contacts B-R open, cutting power to blower
and intermittent pilot control. Burners extinguish and
blower stops. Circulator pump continues to run as long
as the thermostat continues to call for heat. When
boiler water temperature drops past the high limit set
point and through the differential, high limit contacts
B-R close, repeating steps 3-7.
9.
If venting system becomes blocked, blower suction
pressure will drop below the pressure switch set point,
opening the pressure switch contacts and cutting power
to the intermittent pilot control. Burners will extinguish,
but blower will remain powered as long as the
thermostat continues to call for heat. If venting system
clears, steps 4-7 will repeat.
10.
Thermostat is satisfied, ending call for heat. Relay coil
1K is de-energized, opening 1K1 and 1K2 contacts.
Burners extinguish. Blower and circulator pump stop.

SEquENCE OF OpErATION

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