To Turn Off Gas To Unit; Heating Sequence Of Operations - Lennox LS25 Series Installation Instructions Manual

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 - Move switch to OFF
WHITE RODGERS 36H SERIES GAS VALVE
INLET
Two-Stage
PRESSURE
PORT
GAS VALVE SWITCH SHOWN IN OFF POSITION
FIGURE 12
WHITE RODGERS 36G GAS VALVE
Single-Stage
MANIFOLD
PRESSURE
ADJUSTMENT
SCREW
MANIFOLD
PRESSURE
OUTLET
GAS VALVE SWITCH SHOWN IN OFF POSITION.
FIGURE 13
Heating Sequence of Operation
1 - When the thermostat calls for heat, the combustion
2 - Combustion air pressure switch proves inducer
operation before allowing ignition sequence to
start. This switch is factory set and no adjustment is
necessary.
3 - After pre-purge of approximately 30 seconds, the
MANIFOLD
spark ignition is energized and the solenoid valves
PRESSURE
open in the gas valve.
OUTLET
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
MANIFOLD
PRESSURE
automatically repeat steps 3, 4, and 5 after 60
ADJUSTMENT
minutes.
SCREW
NOTE - To interrupt the 60-minute lockout period, move
thermostat from "Heat" to "OFF" then back to "Heat." Heat-
ing 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
INLET
no apparent impingement taking place.
PRESSURE
7 - The ignition control will energize the fan approximately
PORT
30 seconds after ignition is established.
8 - After the thermostat demand is satisfied the gas
valve is closed. Thirty seconds after the demand is
satisfied, the combustion air inducer is shut off.
9 - The ignition control will shut off the system fan
approximately 150 seconds after the gas valve is de-
energize.
Page 21
air inducer starts immediately.