Lennox EL280UHE Series Unit Information page 19

C- Heating Components
1. Ignitor
®
The SureLight ignitor is made of durable silicon nitride. Ig­
nitor longevity is enhanced by controlling voltage to the ig­
nitor. 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 figure 13 for ignitor
location and figure 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 flame sensor is located on the left side of the burner sup­
port. See figure 13. The sensor protrudes into the flame en­
velope of the left-most burner. The sensor can be removed
for service without removing any part of the burners. During
operation, flame is sensed by current passed through the
flame and sensing electrode. The SureLight control allows
the gas valve to remain open as long as flame signal is
sensed. A microamp DC meter is needed to check the
flame signal on the integrated control. See figure 14 and
table 9 for flame signal check and measurement.
3. Gas Valve
The two-stage gas valve (figure 18) is internally redundant
to assure safety shut-off. If the gas valve must be replaced,
the same type valve must be used.
24VAC terminals 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 termi­
nals energizes the valve.
Inlet and outlet pressure taps are located on the valve. A regu­
lator adjustment screw is located on the valve.
LPG change over kits are available from Lennox. Kits include
burner orifices.
4. Flame Rollout Switches (S47)
The EL280UHE(X) is equipped with two rollout switches.
See figure 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 ignition
and closes the gas valve. Rollout can be caused by a
blocked heat exchanger, flue 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 re­
quire no adjustment. Always operate the unit with the burner
box front panel in place. Each burner uses an orifice that is
precisely matched to the burner input. Burners can be re­
moved as a one piece assembly for service. If burner assem­
bly has been removed, it is critical to align center of each
burner to the center of the clamshell when re-installing. See
more detail in Section VI- MAINTENANCE sub-section
NO TAG Heat Exchanger and Burners.
6. Primary Limit Control (S10)
The primary limit (S10) is located in the heating vestibule pan­
el. 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 auto­
matically resets when unit temperature returns to normal. The
switch must reset within three minutes or the SureLight control
will go into Watchguard for one hour. The switch is factory
set and cannot be adjusted. The switch may have a different
set point for each unit model number. See Lennox Repair
Parts Handbook if limit switch must be replaced,
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