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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.
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. If the pilot is not detected within 30 seconds,
the igniter and pilot gas 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.
Figure 6.2: Wiring and Connection Diagram
ELECTRICAL