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To Turn Off Gas to Unit
1 − Set thermostat to lowest level.
2 − Turn off all electrical power to unit if service is to be
performed.
3 − Turn knob on gas valve 90° clockwise
to OFF.
Heating Sequence of Operation
1 − When the thermostat calls for heat, the combustion
air inducer starts immediately.
2 − Combustion air pressure switch proves inducer
operation before allowing power to the ignition
controller. This switch is factory−set and no
adjustment is necessary.
3 − After prepurge of approximately 30 seconds, the
spark ignition is energized and the solenoid valves
open in the gas valve. LF24 models 230, 250, 300,
345 and 400 are equipped with a step opening
valve. During ignition phase of start−up a pressure of
approximately 25% of full rate allows even ignition
of all burners for several seconds before full rate
pressure is established.
4 − The spark then ignites the gas, the ignition sensor
proves the flame, and the combustion process
continues.
5 − In the event that the flame is not detected after the
first 10−second trial for ignition, the controller will
repeat steps 3 and 4 an additional two times before
locking out the gas valve. Ignition control will then
automatically repeat steps 3, 4, and 5 after 60
minutes.
NOTE: To interrupt the 60−minute lockout period, move
thermostat from Heat" to OFF" then back to Heat."
Heating sequence then restarts at step 1.
6 − The burners must light without noticeable crossover
delay. There must be no flame lifting from the burner
heads, flashback or burning within the burner. The
flames should be predominantly blue in color and
should be approximately centered in the tubes with
no apparent impingement taking place.
7 − The ignition control will energize the fan(s)
approximately 45 seconds after ignition is
established.
8 − After the thermostat demand is satisfied, the gas
valve is closed. Five seconds after the demand is
satisfied, the combustion air inducer is shut off.
9 − The ignition control must shut off the system fan
approximately 150 seconds after the gas valve is
de-energized.
Ignition Control LED
The ignition control contains a green LED which indicates
the following:
TABLE 8
IGNITION CONTROL LED
LED UNIT OPERATION
Slow
Flash*
Normal Operation − No call for heat
Fast
Flash
Normal Operation − Call for heat
2
Flashes
System lockout − failed to detect or sustain
flame
3
Flashes
Pressure switch failed closed before CAI is en-
ergized or failed open after CAI is energized
4
Flashes
High limit or rollout switch open
5
Flashes
Flame sensed and gas valve not energized
Steady
Off
Loss of power
Steady
On
Ignition control failure
*When thermostat is placed in continuous fan mode, LED will
slowly flash.
High Altitude Adjustment
In Canada, certification for installation at altitudes over
4500 feet (1372m) above sea level is the jurisdiction of the
local authorities.
Unit may be fired at full input up to 2000 feet (610m) above
sea level. Above 2000 feet (610m), manifold pressure
must be adjusted on some units. Adjust pressure
regulator to pressure shown in table 9 for natural gas and
table 10 for LP/propane gas.
In some cases, it is necessary to change the pressure
switch to ensure proper operation at higher altitudes. See
table 1.
NOTE − A natural to LP/propane gas changeover kit is
required to convert the unit in the field. Refer to the
installation instructions supplied with the changeover kit
for conversion procedure.
If unit is installed at an altitude greater than 7500 feet
(2286m), unit must be derated by four percent for each
additional 1000 feet (305m) above 7500 feet (2286m).
The combustion air inducer proving switch is factory set
and no adjustment is necessary.
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