17
Sequence of Operation - Figure 10, Page 18.
1.
Thermostat calls for heat, control relay contacts.
2.
Circulator pump is powered through terminals C1 and
C2. Control holds off burner and attempts to satisfy
thermostat with residual boiler heat.
3.
Induced draft blower and transformer primary are
powered.
4.
When blower gets up to speed and blower suction
pressure reaches pressure switch set point, pressure
switch contacts close sending 24 volts to pilot control
from transformer secondary.
5.
Pilot gas valve opens and spark initiates to light pilot
burner.
6.
When pilot fl ame 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 open, cutting power to
blower and 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 close,
repeating steps 3-7.
9.
If venting system becomes blocked, blower suction
pressure will drop below pressure switch set point,
opening pressure switch contacts and cutting power to
pilot control. Burners will extinguish, but blower will
remain powered as long as thermostat continues to call
for heat. If venting system clears, steps 4-7 will repeat.
10.
Thermostat is satisfi ed, ending call for heat. Relay coil
is de-energized, opening contacts. Burners extinguish.
Blower and circulator pump stop.
SEQUENCE OF OPERATION
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