REASONS FOR BURNER
LOCKOUT
BURNER NEVER LIGHTS, ZERO
DC µA FLAME CURRENT
1. Damaged igniter.
2. Igniter not positioned in the
flame.
3. Failed gas valve.
4. No gas supply.
5. An open pressure switch.
6. Broken wires.
7. Broken Molex plug or faulty plug
connections.
8. Damaged integrated furnace
control board.
BURNER LIGHTS, ZERO DC µA
FLAME CURRENT
1. Damaged flame sensor.
2.
Extremely low gas pressure.
3. Ungrounded furnace.
4.
Reverse polarity of the power
supply.
5.
Broken Molex plug or faulty plug
connections.
6.
Faulty flame sensor connection.
7.
Flame sensor shorted to furnace
chassis.
8. Damaged integrated furnace
control board.
BURNER LIGHTS, LOW µA FLAME
CURRENT (Less Than 1.5 µA)
1. Damaged integrated furnace
control board.
2. Poorly grounded furnace.
3. Poorly positioned sensor.
4. Low supply voltage.
5. Low gas pressure.
6. Moisture in the Molex plug.
7. Broken Molex plug or faulty plug
connections.
8. Corroded flame sensor.
AIRFLOW
As stated before, one of the most
common causes of heat exchanger
failure is overheating due to low air
flow. Limits that open are usually in
response to low air flow. Measure
the furnace temperature rise to
determine the air flow. An air flow
table is located inside the blower
door.
The causes for a too high
temperature rise are the same
as for tripping limits.
1. A dirty or restricted air filter.
2. A dirty or restricted cooling coil.
3. Undersized or restricted return
air system.
4. Undersized or restricted supply
air system.
5.
A problem affecting the main
blower:
a.
A wrong speed tap selection,
b. Failing motor bearings,
c. Low voltage to the motor,
d. Dirty blower wheel,
e. Wrong motor rotation,
f. Blower wheel slipping on the
motor shaft.
6. Overtiring the furnace with too
much gas pressure.
7. Overtiring the furnace with
incorrect burner orifices.
8. Dirty or restricted secondary
heat exchanger.
CO AND CO
2
LEVELS IN THE
FLUE GASES
The carbon monoxide (CO) or
carbon dioxide (CO
2
)
levels indicate
much about the operation of the
furnace and combustion process.
Use the following procedure to
•
sample the CO and CO
2
levels in the
flue gases.
1. Let the furnace operate for
1
Oto 12 minutes to warm to
normal operating temperature.
BE SURE THE BURNER
COMPARTMENT DOOR IS
IN PLACE.
2. Drill as small a hole as
necessary in the vent pipe near
the furnace. Make the hole in an
inconspicuous location.
3. Make the tests with a CO and
CO
2
tester. Follow the test
equipment manufacturer's
procedures to sample the
flue gas.
A.
CO range:
10 PPM- 250 PPM
B. CO
2
% range: 7.0% - 8.5%
4.
After making the test, seal the
opening in the exhaust pipe.
Use a high temperature sealant
to prevent any flue gas escape.
Possible causes for high CO
2
levels:
•
A. Inadequate combustion air,
B. Poor exhaust pipe design or
sizing,
C.
Overtiring with too much gas
pressure,
D.
Overtiring with incorrect
burner orifices,
E. Recirculation of flue
products.
Possible causes for low CO
2
levels:
A.
Too much combustion air,
B.
Underfiring with too little gas
pressure,
C.
Underfiring with incorrect
burner orifices.
NOTE: If the CO
2
level is within the
normal range, the CO level should
also be within it's normal range.
NOTE: Sooting results from the
same causes as high CO and CO
2
.
•
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