Honeywell 7800 Series Product Data page 17

Fault Code
Fault 18 Flame sensed when the shutter
*Flame Detected* is open and no flame is
expected during PREPURGE.
Fault 19 Flame was lost during MFEP or
*Main Flame Ign.* the first 10 seconds of the RUN
state.
Fault 20 Low Fire Interlock switch failure
*Low Fire Sw. Off* to close during PREPURGE.
Fault 21 Running Interlock fault during
*Running ILK* PREPURGE.
Fault 22 Lockout Interlock fault during
*Lockout ILK* PREPURGE.
Fault 23 Combustion airflow interlock
*Airflow Switch* fault during PREPURGE.
Fault 24 The flame interlock (relay
*Call Service* module) was on when it should
be off.
Fault 25 The flame interlock (relay
*Call Service* module) was off when it should
be on.
Fault 26 The Manual Open Valve Switch
*Man-Open Sw. Off* was off when it should be on
(Device specific).
Table 7. Hold and Fault Message Summary (Continued).
System Failure
17
7800 SERIES S7800A KEYBOARD DISPLAY MODULE
Recommended Troubleshooting
1. Check that flame is not present in the combustion chamber.
Correct any errors.
2. Make sure that the flame amplifier and flame detector are
compatible.
3. Check the wiring and correct any errors. Make sure F and G
wires are in individual conduits and protected from stray noise
pickup.
4. Remove the flame amplifier and inspect the connectors. Reset
the flame amplifier.
5. Reset and sequence the relay module.
6. If the code reappears, replace the flame amplifier and/or the
flame detector.
7. If the fault persists, replace the relay module.
1. Inspect the main fuel valve(s) and connection(s).
2. Make sure the fuel pressure is high enough to supply fuel to
the combustion chamber.
3. Make sure the flame detector is positioned to obtain the
required flame signal strength; reset and recycle.
1. Check wiring and correct any errors.
2. Reset and sequence the relay module.
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 to make sure it
closed properly.
4. Measure the voltage between terminal 18 and L2(N) while in
the Prepurge drive to Low Fire state. Line supply voltage
should be present. If not, the switch adjustment is incorrect
and/or the switch is defective and needs replacing.
5. Reset and sequence the relay module. If line supply voltage
was present between the Low Fire Switch and terminal 18, and
the fault still persists, replace the relay module.
1. Check wiring and correct any errors.
2. Inspect the fan; make sure there is no blockage of the air
intake and that it is supplying air.
3. Make sure the Interlock Switches are working properly and that
all switch contacts are free of contaminants.
4. Reset and sequence the relay module to PREPURGE (place
the Run/Test Switch in the Test position, if available). Measure
the voltage between terminals 7 and L2(N). Line voltage
should be present.
5. If steps 1 through 4 are correct and the fault persists, replace
the relay module.
1. Check for F leadwire routing. Make sure routing is in its conduit
and isolated from noise-producing circuits.
1. Check wiring and correct any errors.
2. Make sure that the Manual Open Valve Switch is fully open.
3. Make sure that the Manual Open Valve Switch is functioning
properly and that the switch contacts are free from
contaminants.
4. Reset and sequence the relay module.
5. Make sure that the Manual Open Valve Switch provides an
electrical path when closed. Verify that the relay module is
receiving power at terminal 17.
6. If steps 1 through 5 are correct and the fault persists, replace
the relay module.
65-0090—4