750-265 52
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. Preignition Interlock is open an accumulative time of
30 seconds.
c. Interlock Start check feature is enabled and the
Interlock String (including Airflow Switch) is closed
for 120 seconds with the controller closed. (jum-
pered or welded Interlock).
d. Pilot Valve Terminal is energized.
e. Main Valve Terminal is energized.
f. Internal system fault occurred.
3. PREPURGE Period:
a. Preignition Interlock opens anytime during
PREPURGE period.
b. Flame signal is detected for 10 seconds accumu-
lated time during PREPURGE.
c. 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.
d. 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.
e. Lockout Interlock (if programmed) does not close
within 10 seconds.
f. Lockout Interlock opens during PREPURGE.
g. Pilot Valve terminal is energized.
h. Main Valve terminal is energized.
i. 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. Low Fire Switch opens (if enabled).
b. Lockout Interlock opens (if enabled).
c. Pilot Valve terminal is not energized.
d. No flame is present at the end of the PFEP, or after
programmed number of retry attempts.
e. Main valve terminal is energized.
f. Internal system fault occurred.
6. MAIN FLAME ESTABLISHING PERIOD (MFEP).
a. Low Fire Switch opens (if enabled).
b. Lockout Interlock opens (if enabled).
c. Pilot valve terminal is not energized.
d. Main valve terminal is not energized.
e. No flame present at the end of MFEP.
f. Internal system fault occurred.
7. RUN Period:
a. No flame is present, or flame is lost (if enabled-lock-
out).
b. Lockout Interlock opens) if enabled).
c. IAS Purge and Ignition enabled and the Interlock
opens.
d. Pilot terminal energized (if programmed as Inter-
rupted 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.
Operational Sequence
Central Heating
INITIATE
The R7910 enters the Initiate sequence on Initial Power up or:
• Voltage fluctuations vary +10%/-15%.
• Frequency fluctuations vary +/-10%.
• If Demand, LCI, or Stat interrupt (open) during the
Prepurge Period.
The Initiate sequence also delays the burner motor from being
energized and de-energized from an intermittent AC line input
or control input.
If an AC problem exist more than 240 seconds a lockout will
occur.
Start-up sequence central heating request (system in
standby):
1. Heat request detected (On Setpoint - On Hysteresis).
2. The DHW pump is switched off to prevent the water in
the DHW tank from being cooled-down.
3. The Circulating pump is switched on. If the “pump off”
function for CH-mode is selected, the pump stays off or
will be switched off.
4. After a system Safe Start Check, the Blower (fan) is
switched on after a dynamic ILK switch test (if enabled).
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