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Troubleshooting: Burner starts and fires, but short cycles (too little heat)
Source
Procedure
Causes
Correction
Heat anticipator set too low
Correct heat anticipator setting.
Thermostat
Check thermostat.
Vibration at thermostat
Correct source of vibration.
Thermostat
Check thermostat.
Thermostat in the path of a
warm air draft
Shield thermostat from draft or
relocate.
Dirty furnace air filters
Clean or replace filter.
Burner running too slow
Increase blower speed to main-
tain proper temp. rise.
Blower motor seized or burned
out
Replace motor.
Connect voltmeter between line
lt
ti
t
i
Blower bearings seized
Replace bearings and shaft.
Limit Control
voltage connections to primary
control (black & white leads). If
Blower wheel dirty
Clean blower wheel.
Limit Control
control (black & white leads). If
burner cycles due to power inter-
ruption it is cycling on limit
Blower wheel in backward
Reverse blower wheel.
ruption, it is cycling on limit.
Wrong motor rotation
Replace with properly rotating
wheel.
Restrictions in return or supply
air system
Correct cause of restriction.
Adjustable limit control set too
low
Reset limit to maximum stop
setting.
Power
If voltage fluctuates, fault is in the
power source Recheck voltage
Loose wiring connection
Locate and secure connection.
Power
power source. Recheck voltage
at the power source.
Low or fluctuating line voltage
Call power company.
Troubleshooting: Burner runs continuously (too much heat).
Source
Procedure
Causes
Correction
Shorted or welded thermostat
contacts
Repair or replace the thermo-
stat.
If burner turns
Stuck thermostat bimetal
Clear obstruction or replace
thermostat.
Thermostat
If burner turns
off, fault is in
the thermostat
Thermostat not level
Level thermostat.
Thermostat
Disconnect
th
t t
the thermostat
circuit.
Shorted thermostat wires
Repair short or replace wires.
thermostat
wires at the pri-
circuit.
Thermostat out of calibration
Replace thermostat.
wires at the pri-
mary control.
Thermostat in cold draft
Correct draft or relocate the
thermostat.
Primary control
If burner does
not turn off,
fault is in the
primary control.
Defective primary control
Replace the defective primary
control.
