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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 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
Blower bearings seized Replace bearings and shaft.
Limit Control
voltage connections to primary
control
black & white leads
. If
Blower wheel dirty Clean blower wheel.
.
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.
If voltage fluctuates, fault is in the
power source Recheck voltage
Loose wiring connection Locate and secure connection.
ower
power source.
ec
ec
vo
tage
at the power source.
Low or fluctuating line voltage Call power company.
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
off, fault is in
Thermostat not level Level thermostat.
Disconnect
t
e t
ermostat
circuit.
Shorted thermostat wires Repair short or replace wires.
thermostat
Thermostat out of calibration Replace thermostat.
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.
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