Honeywell 7800 Series Product Data page 21

Fault Code System Failure
Start Switch was on
Fault 27
during PREPURGE
*Start Switch
(RM7838A, RM7838B
On*
only).
Fault 28
*Pilot Flame Pilot flame failure.
Fail*
Fault 29
*Lockout Lockout Interlock fault.
ILK*
Fault 30
*Running Running Interlock fault.
ILK*
Low Fire Interlock
Fault 31
Switch failure to close
*Low Fire
during RUN (RM7838B
Switch Off*
only).
7800 SERIESS7800A2142 4-Line LCD Keyboard Display Module
Start Switch held on too long.
Check wiring; verify that Start Switch is correctly connected.
Make sure that the Start Switch is functioning properly and
that the switch contacts are free of contaminants.
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.
If steps 1 through 3 are correct and the fault persists, replace
the relay module.
Check pilot valve wiring and operation. Correct any errors.
Check fuel supply.
Check pilot pressure and repeat pilot turndown test.
Check ignition transformer electrode, flame detector, flame
detector sighting and flame amplifier.
If steps 1 through 4 are correct and the fault persists, replace
the relay module.
Check wiring; correct any errors.
Inspect the fan; make sure that there is no blockage of the air
intake and that it is supplying air.
Make sure that the Lockout 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.
Inspect the Running Interlocks, including the Airflow Switch,
and the connections.
Make sure that the Running Interlocks, including the Airflow
Switch, are functioning properly and that switch contacts are
free of contaminants.
Reset and sequence the relay module to PREPURGE. Set the
Run/Test Switch, if available, to Test. Measure the voltage
between
terminal 7 and G (ground). Line voltage should be present.
If steps 1 through 3 are correct and the fault persists, replace
the relay module.
Check wiring; correct any errors.
Reset and sequence the relay module.
Use either the manual motor position to drive the motor to
the Low Fire position, or use the Run/Test Switch option, if
available. Sequence to Run drive to Low Fire and place in the
Test position. Adjust the Low Fire Switch while in this state to
make sure it is closing properly.
While in Run, drive to Low Fire state, measure the voltage
between terminal 18 and G (ground). Line voltage should be
present. If not, the switch adjustment is incorrect and/or the
switch is defective and needs replacement.
Reset and sequence the relay module. If line voltage was
present between the Low Fire Switch and terminal 18 and the
fault persists, replace the relay module.
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