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17. SEQUENCE OF OPERATION FOR FENWAL 35-60 DSI CONTROL
Start up - Heat Mode:
On a call for heat the Fenwal 35-60 control will reset, perform a self check routine, flash the
diagnostic LED for up to four seconds. The gas valve and spark are energized commencing
the trial for ignition period. When flame is detected during the trial for ignition, spark is shutoff
immediately and the gas valve remains energized. The thermostat and main burner flame are
constantly monitored to ensure the system continues to operate properly. When the thermo-
stat is satisfied and the demand for heat ends, the gas valve is de-energized.
Flame Failure - Multi Trial Model:
Should the main burner fail to light, or the flame is not detected during the first trial for ignition
period, the gas valve is de-energized and the control goes through an interpurge delay before
another ignition attempt. The control will attempt two additional ignition trials before going into
lockout and the valve relay is de-energized.
Recovery from lockout requires a manual reset by either resetting the thermostat or removing
24 volts for a period of 5 seconds. If the thermostat is still calling for heat after one hour the
control will automatically reset and attempt to ignite the burner again.
Flame Failure - Re-Ignition:
If the established flame signal is lost while the burner is operating, the control will respond
within 0.8 seconds. The HV spark will be energized for a trial ignition period in an attempt to
relight the burner.
If the burner does not light the control will make two more attempts to relight the burner before
de-energizing the gas valve. If the burner does not relight, the control will go into lockout as
noted above in "Failure to light". If flame is re-established, normal operation resumes. Multi-try
models will allow three trials for ignition including interpurge delay between trials.
Flame current is the current
which passes through the flame
from the sensor to ground. The
minimum flame current neces-
sary to keep the Fenwal 35-60
system from lockout is 0.7 mi-
croamps (µA). To measure the
flame current, connect analog
DC microammeter to the FC-
FC+ terminals.
Meter should read 0.7 µA or
higher. If the meter reads below
"0" on scale, meter leads are
reversed. Disconnect power
and reconnect meter leads for
proper polarity.
continued ...
25
SE+ Series Infrared Gas Heater Installation and Operation Manual
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