PB Heat MI/MIH series - Manual (Page 19)

17
D. SEQUENCE OF OPERATION
1. Standing Pilot (See Figure 6.2 above)
a. The vent damper is continuously powered. On a
call for heat, limit relay R is energized, which
energizes:
● the circulator (when used) through contact
R1, and
● the vent damper operator through contact R2,
provided that the high-limit switch is
closed.
The vent damper operator opens the damper.
b. Once the damper is proven open, the gas valve
energizes, provided that all of the following
conditions are met:
● the pilot thermocouple is proving flame
● the blocked vent switch is closed, and
● the flame rollout switch is closed.
Pilot flame is monitored through the pilot
thermocouple. If pilot flame is lost during a call
for heat, main and pilot gas flow will be shut off.
The valve must then be manually reset by
following the Lighting Instructions mounted on
the jacket panel and included in Section 7 of this
manual.
c. When the call for heat ends:
● Limit relay R de-energizes, which opens
contacts R1 and R2.
● The circulator shuts down.
● The gas valve de-energizes.
● The vent damper closes.
d. If temperature exceeds limit setting, main burners
shut off and circulator continues to operate.
ELECTRICAL
Figure 6.2: Wiring and Connection Diagram – Standing Pilot (Continuous Ignition)