Table 20. Operating Sequence (Normal Heat Cycle)
Step Condition Action
1. Call for
heat
Terminal W is energized
Thermostat calls for heat by energizing terminal W
Control determines whether limit switch is open or closed and if pressure switch is open
Limit switch is open
Control deenergizes gas valve, turns fan/blower motor onto heat speed, and runs venter motor
SSD displays “5”
Control is in soft lockout “L” before returning to normal operation
Pressure switch is closed
SSD displays “4”
Control waits indefinitely for pressure switch to open
Pressure switch is open Control proceeds to step 2
2. Prepurge
Venter motor is energized Control waits for pressure switch to close
Pressure switch not closed
within 30 seconds of venter
motor energizing
SSD displays “3”
Control maintains venter motor energized indefinitely as long as call for heat remains and
pressure switch is open
Pressure switch is proven
closed
Control begins prepurge
Flame is present at any time
during prepurge
Prepurge is restarted
Flame is present long
enough to cause lockout
Control runs venter motor and runs fan/blower motor on heat speed
When flame is no longer sensed, venter motor runs through post-purge and fan/blower motor
runs through selected delay OFF time
Control proceeds to soft lockout but still responds to open limit and flame
SSD displays “6” when lockout is due to undesired flame
Venter motor runs for
20-second prepurge time
Control proceeds step 3
3. Ignition
trial period
Spark and main gas valve
are energized
The venter remains energized
Flame is sensed during first
16 seconds
Control deenergizes spark and proceeds to heat fan/blower on delay
Flame is not sensed during
first 16 seconds
Control deenergizes spark and maintains gas valve energized for additional 1-second flame-
proving period
Flame is not present after
flame-proving period
Control deenergizes gas valve and proceeds with ignition retries as specified in Table 21:
abnormal function Ignition Retry
Flame is present after flame-
proving period
Control proceeds to step 4
4. Fan/blower
ON delay
30 seconds after gas valve
has opened
Control energizes fan/blower motor
Gas valve and venter motor
remain energized
Control proceeds to step 5
5. Steady
heat
Limit switch is closed
Control continuously monitors inputs
Pressure switch is closed
Flame is established
Thermostat call for heat
remains
Thermostat call for heat is
removed
Control deenergizes gas valve and proceeds to steps 6 and 7
6. Post-purge
Thermostat is satisfied
Venter motor remains on for 45-second post-purge period
7. Fan/blower
OFF delay
Fan/blower motor is deenergized after selected fan/blower OFF delay
11. Burner flame is sensed and in 30 seconds after gas valve is energized, fan motor is energized.
12. If flame is extinguished during main burner operation, integrated control system closes main valve and must be
reset by interrupting power to control circuit (refer to lighting instructions provided with heater).
13. TO TURN OFF GAS TO APPLIANCE:
a. Set thermostat to lowest setting.
b. If service is to be performed, turn off all electric power to appliance.
c. Open the access door.
d. Turn gas control switch to OFF or turn knob clockwise to OFF (do not force).
e. Close access door.
Operating Sequences
Table 20 describes the heater’s normal operating sequence. Table 21 describes the heater’s abnormal heat cycle
functions. Table 22 describes the heater’s fault modes. Refer to Table 19 for LED indications.
39
I-UEZ (04-21) 1034347-0
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