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Troubleshooting: Burner starts and fires, but short cycles (too little heat)
Source
Procedure
Causes
Correction
Thermostat
Check thermostat.
Heat anticipator set too low
Correct heat anticipator setting.
Vibration at thermostat
Correct source of vibration.
Thermostat in the path of a
warm air draft
Shield thermostat from draft or
relocate.
Limit Control
Connect voltmeter between line
voltage connections to primary
control (black & white leads). If
burner cycles due to power inter-
ruption, it is cycling on limit.
Dirty furnace air filters
Clean or replace filter.
Temperature rise too high
Check fo proper nozzle size.
Replace nozzle, if necessary.
Check for restrictions and re-
move, if necessary.
Check speed tap jumper and
make sure it is still in factory
position.
Blower motor seized or burned
out
Replace motor.
Blower wheel dirty
Clean blower wheel.
Wrong motor rotation
Replace motor.
Restrictions in return or supply
air system
Correct cause of restriction.
Power
If voltage fluctuates, fault is in the
power source. Recheck voltage
at the power source.
Loose wiring connection
Locate and secure connection.
Low or fluctuating line voltage
Call power company.
Troubleshooting: Burner runs continuously (too much heat).
Source
Procedure
Causes
Correction
Thermostat
Disconnect
thermostat
wires at the pri-
mary control.
If burner turns
off, fault is in
the thermostat
circuit.
Shorted or welded thermostat
contacts
Repair or replace the thermo-
stat.
Stuck thermostat bimetal
Clear obstruction or replace
thermostat.
Thermostat not level
Level thermostat.
Shorted thermostat wires
Repair short or replace wires.
Thermostat out of calibration
Replace thermostat.
Thermostat in cold draft
Correct draft or relocate the
thermostat.
Primary control
If burner does
not turn off,
fault is in the
primary control.
Failed primary control
Replace the primary control.
