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ELECTRICAL
Figure 6.2: Wiring and Connection Diagram
D. SEQUENCE OF OPERATION
1. Thermostat calls for heat, energizes Control Relay (CR).
2. Control Relay (CR) energizes circulator.
3. Limit senses boiler water temperature. Prevents boiler
operation until water temperature falls approximately
°
°
15
F (8
C) below the cut-out temperature.
4. Limit energizes Fan and Isolation Relay (IR).
5. Negative pressure induced by fan switches Pressure
Switch, continuing power through closed contacts
(IR-1) and flame roll-out switch.
6. Gas valve energizes.
a. Igniter on.
b. Pilot gas on, igniting pilot.
16
7. Pilot flame detected.
a. Igniter off.
b. Main gas on, igniting main burners.
Note: If pilot flame is not detected within 30 seconds, the
igniter is turned off for 30 seconds, and then turned back
on for another 30 seconds. If the pilot remains undetected
in this second ignition period, the igniter and pilot are
turned off for 5 minutes. The sequence then resumes at
Step 6a.
8. Call for heat ends.
a. Pilot and main gas off, extinguishing pilot and
main burners.
b. Fan and circulator off.
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