Lennox International Inc. o23v - Manual (Page 26)

Page 26
Troubleshooting: Fan board operating sequence
Action System Response
Thermostat calls for heat.
(W terminal is energized.) Blower control board closes oil primary control T−3T connections.
Ignition system and oil primary control start the furnace. Oil flows as long as oil primary control
senses flame.
Burner motor energized and heat fan on delay timing begins. When timing is complete, the
circulating fan is energized at heat speed and warm air is delivered to the controlled space.
Thermostat ends call for heat.
(W terminal is de−energized.) Oil primary control is de−energized, terminating the burner cycle.
Heat fan off delay timing begins. When timing is complete, circulating fan is de−energized.
Blower control board returns to standby mode (oil primary control and circulating fan are off).
Burner fails to light. Oil primary control locks out within lockout timing (timing depends on oil primary control).
Burner motor is de−energized.
Established flame fails. Burner motor is de−energized and oil primary control goes into recycle mode.
If the fan off delay is longer than the recycle timing, the heat fan continues to run through the
next trial for ignition.
Limit switch opens. Oil primary control shut off the burner.
Circulating fan is energized immediately.
A15 control board opens oil primary control T−3T connections.
Circulating fan runs as long as limit stays open.
Limit switch closes. If there is a heat demand, A15 control board energizes oil primary control, initiating burner light
off.
Troubleshooting: Burner fails to start
Source Procedure Causes Correction
Thermostat Check thermostat settings. Thermostat in OFF or
COOL Switch to HEAT.
Thermostat is set too low Turn thermostat to higher temperature.
Safety
Overloads Check burner motor,
primary safety control, &
auxiliary limit switch Burner motor overload
tripped Push reset button pump motor.
auxiliary limit switch.
Primary control tripped on
safety Reset primary control.
Auxiliary limit switch tripped
on safety Reset auxiliary limit.
Power Check furnace disconnect
switch & main disconnect Open switch Close switch.
switch & main disconnect.
Blown fuse or tripped circuit
breaker Replace fuse or reset circuit breaker.
Thermostat Touch jumper wire across
thermostat terminals on
primary control If burner Broken or loose thermostat
wires Repair or replace wires.
primary control. If burner
starts, then fault is in the
thermostat circuit.
Loose thermostat screw
connection Tighten connection.
thermostat circuit.
Dirty thermostat contacts Clean contacts.
Thermostat not level Level thermostat.
Faulty thermostat Replace thermostat.
CAD Cell Disconnect the flame
detector wires at the
primary control If the Flame detector leads are
shorted Separate leads.
primary control. If the
burner starts, fault is in the
detector circuit.
Flame detector exposed to
light Seal off false source of light.
detector circuit.
short circuit in the flame
detector Replace detector.
table continued on next page