Honeywell S7800A Installation Manual page 18

7800 SERIES S7800A KEYBOARD DISPLAY MODULE
Fault Code
Fault 19
*Main Flame Ign.*
Fault 20
*Low Fire Sw. Off*
Fault 21
*Running ILK*
Fault 22
*Lockout ILK*
Fault 23
*Airflow Switch*
Fault 24
*Call Service*
Fault 25
*Call Service*
Fault 26
*Man-Open Sw. Off*
Fault 27
*Start Switch On*
Fault 28
*Pilot Flame Fail*
65-0090-6
Table 7. Hold and Fault Message Summary. (Continued)
System Failure
Flame was lost during MFEP or
the first 10 seconds of the RUN
state.
Low Fire Interlock switch failure
to close during PREPURGE.
Running Interlock fault during
PREPURGE.
Lockout Interlock fault during
PREPURGE.
Combustion airflow interlock
fault during PREPURGE.
The flame interlock (relay
module) was on when it should
be off.
The flame interlock (relay
module) was off when it should
be on.
The Manual Open Valve Switch
was off when it should be on
(Device specific).
Start Switch was on during
PREPURGE (Device specific).
Pilot flame failure.
Recommended Troubleshooting
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.
1. Start Switch held on too long.
2. Check wiring; verify that Start Switch is correctly connected.
3. Make sure that the Start Switch is functioning properly and that
the switch contacts are free of contaminants.
4. Reset and sequence the relay module to PREPURGE; set the
Run/Test Switch to Test. Make sure there is no power at
terminal 6 during PREPURGE.
5. If steps 1 through 4 are correct and the fault persists, replace
the relay module.
1. Check pilot valve wiring and operation. Correct any errors.
2. Check fuel supply.
3. Check pilot pressure and repeat pilot turndown test.
4. Check ignition transformer electrode, flame detector, flame
detector sighting and flame amplifier.
5. If steps 1 through 4 are correct and the fault persists, replace
the relay module.
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