69-0924—2
8
S8921D HOT SURFACE IGNITION MODULE
Fig. 4. S8921D troubleshooting sequence.
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
START
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
NO
NO
YES
YES
YES
YES
M7598
SET THERMOSTAT TO
CALL FOR HEAT
LED PULSES WITH
“HEARTBEAT”
IGNITER WARMS UP
AND GLOWS RED
COMBUSTION BLOWER
ENERGIZED
MAIN BURNER LIGHTS
MAIN BURNER REMAINS
LIT AFTER TRIAL FOR
IGNITION ENDS
SYSTEM RUNS UNTIL
CALL FOR HEAT ENDS
END CALL FOR HEAT.
COMBUSTION AIR BLOWER
AND GAS CONTROL OFF.
TROUBLESHOOTING ENDS
WARNING
ELECTRICAL SHOCK HAZARD MAY CAUSE SERIOUS INJURY OR DEATH.
Dangerous line voltage is exposed during troubleshooting. Disconnect power before
touching control. Service must be by trained, experienced service technician.
Check for 24 Vac across ignition module 24V and 24V(GND) terminals.
Replace Module.
• Check line voltage power.
• Check low voltage transformer.
• Check limits and safety controls (closed).
• Check thermostat.
• Check system wiring to ignition module.
Check for 120 Vac across
module HSI terminals.
Check air proving
switch (open)
NO
• Check/replace wiring to igniter.
• Check/replace igniter.
YES
Replace module
Check air proving switch (open).
Replace air proving switch
Replace air proving switch
Check for 120 Vac across module
CAB terminals.
Replace module
• Check/replace wiring to combustion air blower.
• Check/replace combustion air blower.
Check air proving switch is closed.
• Check for blocked vent.
• Replace air proving switch.
• Remove call for heat.
• Check that external gas shutoff and gas control manual valves are OPEN (ON).
• Check igniter position.
• Connect AC voltmeter across VALVE and VALVE(GND) terminal of module.
• Re-establish call for heat.
• Check for 24 Vac across VALVE and VALVE(GND) terminals during trial for ignition.
Note: Voltage present only during trial for ignition after air proving switch confims
combustion air flow.
Replace module
• Check/replace wiring to gas control.
• Check/replace gas control.
Note: Ignition module will continue ignition cycle to lockout (after 5 trials for ignition).
Troubleshooting may be accomplished best by recycling the call for heat.
• Check continuity of ground wire and ground path from main burner to GND (BURNER) terminal of igniter module.
• Check that burner flame covers flame sensor (see Fig. 3).
• Check insulation on flame sensor leads.
• Check that manifold gas pressure stays at recommended level as burner runs.
• Check flame sensor for contamination or damage. Replace if necessary.
• Check insulation on sensor leads and check sensor position.
• If checks are okay, replace the igniter module.
NOTE: SYSTEM FAILURE AFTER MAIN FLAME HAS LIT HAS A LOW PROBABILITY OF BEING THE
IGNITER MODULE.
Note: If igniter module goes into lockout, reset system.
• Check continuity of ground wire and ground path from main burner to GND (BURNER) terminal.
Note: If ground is poor or erratic, shutdowns can occur occasionally even though operation is normal at the time
of checkout.
• Check for excessive heat at flame sensor ceramic base (temperature above 1000
°
F (538
°
C) causes short to ground).
• Check for intermittent low manifold gas pressure due to other gas appliances firing, restricted gas piping, or low gas
utility gas supply pressure.
If checks are okay, replace igniter module.
NOTE: SYSTEM FAILURE DURING A RUN CYCLE HAS LIT HAS A LOW PROBABILITY OF BEING THE
IGNITER MODULE.
• Check for proper thermostat operation.
• Check gas control, replace if necessary.
Repeat procedure until trouble-free operation is obtained.