Honeywell 7800 Series Product Data page 20

7800 SERIESS7800A2142 4-Line LCD Keyboard Display Module
Fault Code System Failure
Flame was lost during
Fault 19
MFEP or the first 10
*Main Flame
seconds of the RUN
Ignition*
state.
Fault 20 Low Fire Interlock
*Low Fire switch failure to close
Switch Off* during PREPURGE.
Fault 21
Running Interlock fault
*Running
during PREPURGE.
ILK*
Fault 22
Lockout Interlock fault
*Lockout
during PREPURGE.
ILK*
Combustion airflow
Fault 23 *Air-
interlock fault during
flow Switch*
PREPURGE.
The flame interlock
Fault 24 *In-
(relay module) was on
ternal fault*
when it should be off.
The flame interlock
Fault 25 *In-
(relay module) was off
ternal fault*
when it should be on.
The Manual Open
Fault 26
Valve Switch was off
*Man-Open
when it should be on
Sw. Off*
(RM7838B only).
32-00110-07
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 con-
duit 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 contam-
inants.
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.
20