Honeywell 7800 Series Manual page 12

7800 SERIES RELAY MODULES
Fault Code
Fault 18 Flame sensed when shutter is
*Flame Detected* 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
(RM7838B only).
65-0229—1
Table 3. Hold and Fault Message Summary (continued).
System Failure
1.
2.
3.
4.
5.
6.
7.
1.
2.
3.
1.
2.
3.
4.
5.
1.
2.
3.
4.
5.
1.
1.
2.
3.
4.
5.
6.
Recommended Troubleshooting
Check that flame is not present in the combustion chamber.
Correct any errors.
Make sure that the flame amplifier and flame detector are
compatible.
Check the wiring and correct any errors. Make sure F and G
wires are in individual conduits and protected from stray
noise pickup.
Remove the flame amplifier and inspect the connectors.
Reseat the flame amplifier.
Reset and sequence the relay module.
If the code reappears, replace the flame amplifier and/or the
flame detector.
If the fault persists, replace the relay module.
Inspect the main fuel valve(s) and connection(s).
Make sure that the fuel pressure is high enough to supply
fuel to the combustion chamber.
Make sure the flame detector is positioned to obtain the
required flame signal strength; reset and recycle.
Check wiring and correct any errors.
Reset and sequence the relay module.
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 that it closes properly.
Measure the voltage between terminal 18 and G (ground)
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.
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.
Check wiring; correct any errors.
Inspect the fan; make sure there is no blockage of the air
intake and that it is supplying air.
Make sure the Interlock Switches are working properly and
that all switch contacts are free of contaminants.
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 G (ground).
Line voltage should be present.
If steps 1 through 4 are correct and the fault persists,
replace the relay module.
Check for F leadwire routing. Make sure routing is in its
conduit and isolated from noise-producing circuits.
Check wiring and correct any errors.
Make sure that the Manual Open Valve Switch is fully open.
Make sure that the Manual Open Valve Switch is
functioning properly and that the switch contacts are free
from contaminants.
Reset and sequence the relay module.
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.
If steps 1 through 5 are correct and the fault persists,
replace the relay module.
12
(continued)