PeerlessBoilers PSC II, Installation, Operation & Maintanance Manual

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19
ELECTRICAL
D. BOILER SEQUENCE OF OPERATION
1. Thermostat calls for heat.
2. Limit control energizes circulator.
3. Limit control energizes B1 circuit if boiler water
temperature is below setpoint minus differential.
Setpoint is calculated according to thermostat cycle
and economy/efficiency setting. See limit control
literature for further information.
4. BR relay energizes blower.
5. Negative pressure induced by blower switches
Pressure Switch, continuing power through closed
contacts (BR-2) and flame roll-out switch.
6. Gas valve energizes.
a. Ignitor on.
b. Pilot gas on, igniting pilot
7. Pilot flame detected.
a. Ignitor off.
b. Main gas on, igniting main burners.
Note: If pilot flame is not detected within 90 seconds,
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. Blower and circulator off.