507651-01
Page 26 of 32
Issue 1907
Failure to Operate
If the unit fails to operate, check the following:
1. Is the thermostat calling for heat?
2. Are access panels securely in place?
3. Is the main disconnect switch closed?
4. Is there a blown fuse or tripped circuit breaker?
5. Is the filter dirty or plugged? Dirty or plugged filters will
cause the limit control to shut the unit off.
6. Is gas turned on at the meter?
7. Is the manual main shut-off valve open?
8. Is the internal manual shut-off valve open?
9. Is the unit ignition system in lock out? If the unit locks
out again, call the service technician to inspect the unit
for blockages.
10. Is pressure switch closed? Obstructed flue will cause
unit to shut off at pressure switch. Check flue and
outlet for blockages.
11. Are flame rollout switches tripped? If flame rollout
switches are tripped, call the service technician for
inspection.
Heating Sequence of Operation
1. When thermostat calls for heat, combustion air blower
starts.
2. Combustion air pressure switch proves blower
operation. Switch is factory-set and requires no
adjustment.
3. After a 15-second prepurge, the hot surface ignitor
energizes.
4. After a 20-second ignitor warm-up period, the gas
valve solenoid opens. A 4-second trial for ignition
period begins.
5. Gas is ignited, flame sensor proves the flame, and the
combustion process continues.
Gas Pressure Adjustment
Gas Flow (Approximate)
Table 8.
Gas Meter Clocking Chart
Model
Seconds for One Revolution
Natural Gas
1 cu ft Dial
2 cu ft Dial
-040
90
180
-060
60
120
-080
45
90
-100
36
72
Natural - 1000 btu/cu ft
Furnace should operate at least 5 minutes before checking
gas flow. Determine time in seconds for two revolutions of
gas through the meter. Two revolutions assures a more
accurate time. Divide by two and compare to time in
Table 8. If manifold pressure matches Table 9 and rate is
incorrect, check gas orifices for proper size and restriction.
Remove temporary gas meter if installed.
NOTE:
To obtain accurate reading, shut off all other gas
appliances connected to meter.
6. If flame is not detected after first ignition trial, the
ignition control will repeat steps 3 and 4 four more times
before locking out the gas valve (“WATCHGUARD”
flame failure mode). The ignition control will then
automatically repeat steps 1 through 6 after 60
minutes.
7. To interrupt the 60-minute “WATCHGUARD” period,
move thermostat from “Heat” to “OFF” then back to
“Heat.” Heating sequence then restarts at step 1.
