750-166 2-11
TABLE 4—FAULT MESSAGE AND RECOMMENDED TROUBLESHOOTING (Continued).
Fault Code System Failure Recommended Troubleshooting
Fault 18
*Flame Detected*
Flame sensed when shutter open
and no flame is expected during
Prepurge.
1. Check that flame is not present in the combustion
chamber. Correct any errors.
2. Assure that the flame amplifier and flame
detector are compatible.
3. Check wiring; correct any errors.
4. Remove the flame amplifier and inspect the
connectors. Reseat the flame amplifier.
5. Reset and sequence the CB 780/CB 784.
6. If the code reappears, replace the flame amplifier
and/or the flame detector.
7. If the fault persists, replace the relay module.
Fault 19
*Main Flame Ign.*
Flame was lost during MFEP or
the first 10 seconds of the Run
state.
1. Inspect the main fuel valve(s) and connections.
2. Verify that the fuel pressure is sufficient to
supply fuel to the combustion chamber. Inspect
the connections to the fuel pressure switches to
assure proper functioning.
3. Inspect the Airflow Switch to assure proper
functioning.
4. Check the flame detector sighting position; reset
and cycle. Measure flame signal strength. Does it
meet specifications? If not, refer to the flame
detector and/or flame amplifier checkout
procedures in the installation instructions.
Fault 20
*Low Fire Sw. Off*
Low fire interlock switch failure
to close during Prepurge.
1. Check wiring; correct any errors.
2. Reset and sequence the CB 780/CB 784.
3. Use either the manual motor potentiometer to
drive the motor to the Low Fire position, or use
the Run/Test switch option (if available)
sequence to Prepurge Drive to Low Fire and
place in the TEST position. Adjust the Low Fire
switch while in this state to assure that it is
closing properly.
4. While in the Prepurge Drive to Low Fire state,
measure the voltage between terminal 19 and
G (ground). 120 Vac should be present. If not,
the switch adjustment is incorrect and/or the
switch is defective and should be replaced.
5. Reset and sequence the CB 780/CB 784. If
120 Vac was present between the Low Fire
switch and terminal 19 and the fault still persists,
replace the relay module.
Fault 22
*Lockout ILK*
Lockout Interlock fault during
Prepurge.
1. Check wiring; correct any errors.
2. Inspect the fan; assure that there is no blockage
of the air intake and that it is supplying air.
3. Assure that the Lockout Interlock switches are
functioning properly and that the contacts are
free from contaminants.
4. Reset and sequence the CB 780/CB 784 to
Prepurge (place the Run/Test switch into the
TEST position, if available). Measure the voltage
between terminal 7 and G (ground). 120 Vac
should be present.
5. If steps 1 through 4 are correct and the fault
persists, replace the relay module.
(Continued)
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