Lennox gas heater troubleshooting

ThermostatCheck thermostat settings.Thermostat in OFF or COOLSwitch to HEAT.
Thermostat is set too lowTurn thermostat to higher temperature.
Safety OverloadsCheck burner motor, primary safety control, & auxiliary limit switch.Burner motor overload trippedPush reset button pump motor.
Primary control tripped on safetyReset primary control.
Auxiliary limit switch tripped on safetyReset auxiliary limit.
PowerCheck furnace disconnect switch & main disconnect.Open switchClose switch.
Blown fuse or tripped circuit breakerReplace fuse or reset circuit breaker.
ThermostatTouch jumper wire across thermostat terminals on primary control. If burner starts, then fault is in the thermostat circuit.Broken or loose thermostat wiresRepair or replace wires.
Loose thermostat screw connectionTighten connection.
Dirty thermostat contactsClean contacts.
Thermostat not levelLevel thermostat.
Faulty thermostatReplace thermostat.
CAD CellDisconnect the flame detector wires at the primary control. If the bumer starts, fault is in the detector circuit.Flame detector leads are shortedSeparate leads.
Flame detector exposed to lightSeal off false source of light.
short circuit in the flame detectorReplace detector.
Primary ControlPlace trouble light between the black and white leads. No light indicates that no power is going to the control.Primary or auxiliary control switch is openCheck adjustment. Set the maximum setting.
Jumper terminals; if burner starts, switch is faulty, replace control.
Open circuit between disconnect switch and limit controlTrace wiring and repair or replace it.
Low line voltage or power failureCall the power company.
Place trouble light between the orange and white leads. No light indicates faulty control.Defective internal control circuitReplace the control.
BurnerPlace the trouble light between the black and white leads to the burner motor. No light indicates that no power is getting to the motor.Blown fuseReplace the fuse.
Place trouble light between the black and white leads to the blower motor. Light indicates power to the motor and bumer fault.Binding bumer blower wheelTurn off power and rotate the blower wheel by hand. If seized, free the wheel or replace the fuel pump.
Sized fuel pump
Defective burner motorReplace the motor.
Oil SupplyCheck tank gauge or use dip stick.No oil in tankFill tank.
Coat dip stick with litmus paste and insert into bottom of tank.Water in oil tankIf water depth exceeds 1 inch, pump or drain water.
Listen for pump whine.Tank shut-off valve closedOpen valve.
Oil Filters & Oil LineListen for pump whine.Oil line filter is pluggedReplace filter cartridges.
Kinks or restriction in oil lineRepair or replace oil line.
Plugged fuel pump strainerClean strainer or replace pump.
Open bleed valve or gauge port. Start the bumer. No oil or milky oil indicates loss or prime.Air leak in oil supply lineLocate and correct leak.
Tighten all connections.
Oil PumpInstall pressure gauge on pump and read pressure. Should not be less than 140 psi.Pump is partially or completely frozen. No pressure and the motor locks out on overload.Replace pump.
Coupling disengaged or broken no pressureRe-engage or replace coupling.
Fuel pressure too lowAdjust to 100 psi.
NozzleDisconnect ignition leads. Observe the oil spray (gun assembly must be removed from unit). Inspect the nozzle for plugged orifice or carbon build-up around orifice.Nozzle orifice pluggedReplace nozzle with the same size, spray angle, and spray type.
Nozzle strainer plugged
Poor or off center spray
Ignition ElectrodesRemove gun assembly and inspect electrodes and leads.Fouled or shorted electrodesClean electrode leads.
Dirty electrodes and leads
Eroded electrode tipsClean electrode tips and reset the gap to 5/32 inches and correctly position tips.
Improper electrode gap spacing
Bad buss bar connectionRetension and realign.
Cracked or chipped insulatorsReplace electrode.
Cracked or burned lead insulatorsReplace electrode leads.
IgnitionConnect ignition leads to the transformer. Start burner and observe spark. Check line voltage to transformer primary.Low line voltageCheck voltage at power source. Correct cause of voltage drop or call the power company.
TransformerBurned out transformer windings.Replace the transformer.
No spark or weak sparkProperly ground the transformer case.
Bumer MotorMotor does not come up to speed and trips out on overload. Turn off power and rotate blower wheel by hand to check for binding or excessive drag.Low line voltageCheck voltage at power source. Correct cause of voltage drop or the call power company.
Pump or blower overloading motorCorrect cause of overloading.
Faulty motorReplace motor.
ThermostatCheck thermostat.Heat anticipator set too lowCorrect heat anticipator setting.
Vibration at thermostatCorrect source of vibration.
Thermostat in the path of a warm air draftShield thermostat from draft or relocate.
Limit ControlConnect voltmeter between line voltage connections to primary control (black & white leads). If bumer cycles due to power interruption, it is cycling on limit.Dirty furnace air filtersClean or replace filter.
Burner running too slowIncrease blower speed to maintain proper temp. rise.
Blower motor seized or burned outReplace motor.
Blower bearings seizedReplace bearings and shaft.
Blower wheel dirtyClean blower wheel.
Blower wheel in backwardReverse blower wheel.
Wrong motor rotationReplace with properly rotating wheel.
Restrictions in return or supply air systemCorrect cause of restriction.
Adjustable limit control set too lowReset limit to maximum stop setting.
PowerIf voltage fluctuates, fault is in the power source. Recheck voltage at the power source.Loose wiring connectionLocate and secure connection.
Low or fluctuating line voltageCall power company.