SYSTEM OPERATION
32
HEATING - Abnormal Operation
The following presents the probable causes of question-
able furnace operation and how to fix them. Look through
the observation window in the blower access door and make
a note of the number of flashes in sequence between pauses.
Next, refer to the
Troubleshooting Chart
on the following
pages for an interpretation of the LED signals and to the
information in this section for a description of the problem.
1.
Internal Control Failure with Integrated Ignition
Control.
Check for voltage to the furnace and low volt-
age at the control board. Check for blown fuse on the
control board. If the control determines it has an inter-
nal fault, it enters a locked-out state. Any of the situa-
tions mentioned will cause the diagnostic LED to pro-
vide
no signal.
The control board should only be re-
placed after all other checks from the
Troubleshooting
Chart
have been verified.
2.
System Lockout.
If a flame is not sensed during the
first seven (4) seconds after the gas valve is energized,
the control turns off the gas. There will then be a 30
second delay while the induced draft blower is ener-
gized to purge the heat exchanger. The ignitor will next
be energized and preheated. The gas valve will then be
energized. If flame is not sensed in seven (4) seconds
the gas valve will be de-energized and another purge
will occur. The control will cycle the gas valve a total of
three (3) times before it determines it cannot establish
measurable combustion and enters a locked out state.
The diagnostic light code for this problem is
one short
flash
followed by a longer pause. The control can be
reset and brought out of lockout mode by turning the
thermostat off for more than (5) seconds and less than
(20) seconds and then back on. It can also be reset by
turning off the electrical disconnect switch to the fur-
nace for a minimum of 5 seconds.
NOTE:
The control board will automatically reset one hour
after lockout occurs. If the furnace frequently has to be
reset, it means that a problem exists that should be cor-
rected. Refer to
Troubleshooting Chart
on the following
pages for aid in determining the cause.
3.
Pressure Switch Stuck Closed.
If the control senses
the pressure switch is closed when the induced draft
blower is off, it waits until the fault is corrected. The
diagnostic light code for this problem is 2
flashes
. The
probable cause is either a faulty pressure switch or
wiring.
4.
Pressure Switch Stuck Open.
If, after the induced
draft blower is energized, the pressure switch does not
close within 5 minutes, the control will go into a 1-hour
lockout. The control will automatically reset from lock-
out and restart the ignition sequence. The diagnostic
light code for this problem is
three short flashes
fol-
lowed by a pause. The probable causes are either dis-
connected hose to the pressure switch, faulty pres-
sure switch or wiring, or restricted air intake or flue pip-
ing.
5.
Open Primary or Auxiliary Limit.
If the limit control
opens, the air circulator blower will be turned on until the
limit closes. The induced draft blower will turn off for 5
seconds then turn off. The diagnostic light code for this
problem is
four short flashes
followed by a pause. The
probable cause is either low conditioned air flow due to
dirty filter or resistance in duct work, faulty limit, faulty
blower, or blower speed set to low.
6.
Flame Sensed with No Call for Heat.
If the control
senses a flame when the gas valve is de-energized, it
will run the air circulation blower and the induced draft
blower continuously with no further furnace operation.
The diagnostic flash code for this is a
five flashes
. The
probable causes are either a short to ground in flame
sense circuit, miswiring, lingering burner flame or a slow
closing gas valve.
7.
Open Rollout Limit/Open Control Board Fuse.
If the
rollout control opens, the air circulator blower will be en-
ergized all the time. The diagnostic light code for this
problem is
six flashes
followed by a pause. The prob-
able cause is either restricted flue piping or improper air
requirements.
8.
Low Flame Sense Signal.
If the furnace continues to
operate and the micro-amp signal from the flame sensor
falls below specified level, the diagnostic light code for
this problem will be
seven flashes
followed by a pause.
The probable cause is either a coated/oxidized sensor,
incorrectly positioned sensor in burner flame or lazy
burner flame due to improper gas pressure or combus-
tion air.
9.
Igniter circuit or poor ground.
Improperly connected
igniter, bad igniter or poor ground to the equipment. The
diagnostic light code for this problem is
eight flashes
.
Combustion Quality
Combustion quality can be affected by several factors. Major
factors are venting and draining.
Venting
The venting system should be planned and installed with
the following in mind;
•
Should not be longer than necessary
•
Use 45°elbows rather than 90° elbows when possible
•
Must not sag or otherwise trap condensate
•
Use longest radius fittings possible
•
If using 3" venting, make the transition from 2" to 3"
as close as practically possible
•
Make sure there is no flue gas recirculation into the
combustion air pipe
Condensate Drainage
Furnace combustion can be affected if a furnace is holding
condensate. Check for proper connections of drain hoses,
make sure furnace condensate trap is clean. Make sure
