Burner Control Operation - A.O. Smith 100 Series Service Handbook

BURNER CONTROL OPERATION

Safety Shutdown of Burner Control Functions
Safety Shutdown (Lockout) occurs if any of the following occur during the indicated period:
1. INITIATE PERIOD:
a. A/C line power errors occurred.
b. Four minute INITIATE period has been exceeded.
2. STANDBY PERIOD:
a. Flame signal is present after 240 seconds.
b. Main Valve Terminal is energized.
c. Internal system fault occurred.
3. PREPURGE PERIOD:
a. Flame signal is detected for 10 seconds accumulated time during PREPURGE.
b. Purge Rate Fan RPM or High Fire Switch fails to close within four minutes and fifteen seconds after the firing rate motor is
commanded to drive to the high fire position at the start of PREPURGE.
c. Light off Rate Fan RPM or Low Fire Switch fails to close within four minutes and fifteen seconds after the firing rate motor is
commanded to drive to the low fire position at the end of PREPURGE.
d. Lockout Interlock (if programmed) does not close within 10 seconds.
e. Lockout Interlock opens during PREPURGE.
f. Main Valve terminal is energized.
g. Internal system fault occurred.
4. PRE-IGNITION TIME:
a. Lockout Interlock opens.
b. IAS Purge and Ignition enabled and the Interlock opens.
c. Preignition Interlock opens.
d. Pilot Valve terminal is energized.
e. Main Valve terminal is energized.
5. PILOT FLAME ESTABLISHING PERIOD. (PFEP):
a. Lockout Interlock opens (if enabled).
b. Pilot Valve terminal is not energized.
c. No flame is present at the end of the PFEP, or after programmed number of retry attempts.
d. Main valve terminal is energized.
e. Internal system fault occurred.
6. MAIN FLAME ESTABLISHING PERIOD. (MFEP):
a. Lockout Interlock opens (if enabled).
b. Pilot valve terminal is not energized.
c. Main valve terminal is not energized.
d. No flame present at the end of MFEP.
e. Internal system fault occurred.
7. RUN PERIOD:
a. No flame is present, or flame is lost (if enabled-lockout).
b. Lockout Interlock opens) if enabled).
c. IAS Purge and Ignition enabled and the Interlock opens.
d. Pilot terminal energized (if programmed as Interrupted Pilot).
e. Main valve terminal is not energized.
f. Internal system fault occurred.
8. POSTPURGE PERIOD:
a. Preignition Interlock does not close in five seconds.
b. Pilot Valve terminal is energized.
c. Main Valve terminal is energized.
d. Internal system fault occurred.
e. Flame sensed 240 seconds accumulated time after the RUN period.
40 Servicing should only be performed by a Qualified Service Agent