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17
SEQUENCE OF OPERATION
NORMAL OPERATION
1. When THERMOSTAT calls for heat, the VENT
DAMPER is opened (see Paragraphs 17A through
17D). When the damper blade reaches the fully open
position, the GAS VALVE powers the igniter circuit
and opens the pilot valve.
2. The sensing circuit between the Q3450 or Q3480 pilot
and the GAS VALVE proves presence of pilot flame.*
3. The GAS VALVE de-energizes the igniter and opens
the main valve, allowing main gas to flow and
ignition of main burners.
4. On Boilers equipped with Circulators that are wired to
run continuously and, where condensation of flue gas
is encountered in boiler flues, a REVERSE ACTING
CIRCULATOR CONTROL should be installed to stop
the Circulator before the Boiler Water Temperature
drops to that at which flue gas condensation may
occur.
5. The Burners will operate until the THERMOSTAT is
satisfied.
6. After the THERMOSTAT is satisfied the GAS
VALVE will be de-energized. The Main Burners and
Pilot Burner will be extinguished. If Boiler is
equipped with circulator, Circulator will continue to
run. The VENT DAMPER will close (see Paragraph
17E).
SAFETY SHUTDOWN
1. High Limit Switch
In the event excessive boiler water temperature is
developed, the High Limit will open, interrupting
power to the IGNITION MODULE and the DUAL
COMBINATION GAS VALVE. Main Burners and
Pilot Burner will be extinguished immediately and the
vent damper will close. Normal operation will be
resumed when the Boiler Water Temperature drops to
a point where the High Limit Switch closes.
2. Blocked Vent Switch
In the event excessive blockage in the vent system is
developed the blocked vent switch will open interrupt-
ing power to the ignition module and dual combina-
tion gas valve. Main burners and pilot burner will be
extinguished immediately and the vent damper will
close. The source of blockage must be corrected by
trained and skilled personnel from a qualified service
agency before resetting switch.
3. Flame Rollout Switch
In the event excessive blockage in the boiler section
flue passageways is developed the flame rollout switch
will open interrupting power to the ignition module
and the dual combination gas valve. Main burners and
pilot burner will be extinguished immediately and the
vent damper will close. If the flame rollout switch is
activated do not attempt to place the boiler in opera-
tion. The source of blockage must be corrected and the
flame rollout switch replaced by trained and skilled
personnel from a qualified service agency.
4. Pilot
A. Any pilot failure on the Q3450 or Q3480 pilot will
close the main gas valve and energize the igniter.
B. If the igniter breaks or becomes disconnected, the pilot
valve coil loses power, closing the pilot valve.
5. For TROUBLE SHOOTING GUIDE, see Figure 28.
* · SV9500 and SV9600 Gas Valves:
The igniter and pilot gas valve will stay energized
until either the pilot lights or the call for heat ends.
· SV9501 and SV9601 Gas Valves:
If the pilot fails to light after a 90 second trial for
ignition, the igniter will be de-energized and the pilot
gas valve will close. After a 5 minute delay, the
igniter will be re-energized and the pilot gas valve will
re-open. This continuous retry cycle will end either
when the pilot lights or the call for heat ends.