Page 19
C- Heating Components
1. Ignitor
The SureLight® ignitor is made of durable silicon nitride.
Ignitor longevity is enhanced by controlling voltage to the
ignitor. The integrated control provides a regulated 120
volts to the ignitor for a consistent ignition and long ignitor
life. Ohm value should be 39 to 70. See gure 13 for ignit-
or location and gure 15 for ignitor check out.
NOTE - The EL280UHE(X) furnace contains electronic
components that are polarity sensitive. Make sure that the
furnace is wired correctly and is properly grounded.
2. Flame Sensor
A ame sensor is located on the left side of the burner
support. See gure 13. The sensor protrudes into the
ame envelope of the left-most burner. The sensor can
be removed for service without removing any part of the
burners. During operation, ame is sensed by current
passed through the ame and sensing electrode. The
SureLight control allows the gas valve to remain open as
long as ame signal is sensed. A microamp DC meter is
needed to check the ame signal on the integrated con-
trol. See gure 14 and table 9 for ame signal check and
measurement.
3. Gas Valve
The two-stage gas valve (gure 18) is internally redun-
dant to assure safety shut-o. If the gas valve must be
replaced, the same type valve must be used. 24VAC ter-
minals and ON/OFF switch are located on the valve. A
wire harness connects the terminals from the gas valve to
the electronic ignition control. 24V applied to the terminals
energizes the valve.
Inlet and outlet pressure taps are located on the valve. A
regulator adjustment screw is located on the valve. LPG
change over kits are available from Lennox. Kits include
burner orices.
4. Flame Rollout Switches (S47)
The EL280UHE(X) is equipped with two rollout switches.
See gure 13 for location. The limits are a N.C. SPST
manual-reset limit. When S47 senses rollout, the circuit
breaks and the ignition control immediately stops igni-
tion and closes the gas valve. Rollout can be caused by
a blocked heat exchanger, ue or lack of combustion air.
The switches are factory set to trip (open) at 210°F and
cannot be adjusted. To manually reset a tripped switch,
push the reset button located on the control.
5. Burners
All units use inshot burners. Burners are factory set and
require no adjustment. Always operate the unit with the
burner box front panel in place. Each burner uses an ori-
ce that is precisely matched to the burner input. Burners
can be removed as a one piece assembly for service. If
burner assembly has been removed, it is critical to align
center of each burner to the center of the clamshell when
re-installing.
6. Primary Limit Control (S10)
The primary limit (S10) is located in the heating vestibule
panel. When excess heat is sensed in the heat exchanger,
the limit will open. If the limit is open, the furnace control
energizes the supply air blower and closes the gas valve.
The limit automatically resets when unit temperature re-
turns to normal. The switch must reset within three min-
utes or the SureLight control will go into Watchguard for
one hour. The switch is factory set and cannot be adjust-
ed. The switch may have a dierent set point for each unit
model number. See Lennox Repair Parts Handbook if limit
switch must be replaced.
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