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Fig. 15—S8660, S8670 troubleshooting guide.
16
Check continuity of ignition cable and ground wire.
NOTE: If ground is poor or erratic, shutdowns may occur occasionally even though operation is normal at the
time of checkout.
If checks are okay, replace module.
M1173C
START
Check line voltage power, low voltage transformer, limit controller, thermostat and wiring. Also, check air
proving switch on combustion air blower system and that vent damper (if used) is open and end switch is
made.
NOTE: Before troubleshooting, familiarize yourself with the startup and checkout procedure.
NO
TURN GAS SUPPLY OFF.
TURN THERMOSTAT TO
CALL FOR HEAT
POWER TO MODULE
(24V NOMINAL)
YES
Replace S8670.
NO
45 SECOND
DELAY
YES
SPARK ACROSS
IGNITER/SENSOR GAP
Pull ignition lead and check
spark at S8670.
Replace module.
Spark okay?
Check ignition cable, ground wiring, ceramic insulator and gap, and correct.
Check boot of the ignition cable for signs of melting or buckling. Take protective action to shield cable and
boot from excessive temperatures.
YES
YES
Check that all manual gas cocks are open, supply tubing and pressures are good, and pilot burner orifice is
not blocked.
Check electrical connections between module and pilot operator on gas control.
Check for 24 Vac across PV-MV/PV terminals on module; If voltage is okay, replace gas control; if no
voltage, replace module.
NO
TURN GAS SUPPLY ON
YES
PILOT BURNER LIGHTS?
NO
SPARK STOPS WHEN
PILOT IS LIT?
YES
NOTE: If module goes into lockout, reset system.
Check continuity of ignition cable and ground wire.
Clean flame rod.
Check electrical connections between flame rod and module.
Check for cracked ceramic flame rod insulator.
Check that pilot flame covers flame rod and is steady and blue.
Adjust pilot flame.
If checks are okay, replace module.
NO
MAIN BURNER LIGHTS?
YES
Check for 24 Vac (nominal) across MV-MV/PV terminals. if no voltage, replace module.
Check electrical connections between module and gas control. If okay, replace gas control.
NO
SYSTEM RUNS UNTIL
CALL FOR HEAT ENDS?
YES
NOTE: If module goes into lockout, reset system.
Check for proper thermostat (controller) operation.
Remove MV lead at module; if valve closes, recheck temperature controller and wiring; if not, replace gas
control.
NO
CALL FOR HEAT ENDS
YES
SYSTEM SHUTS OFF?
TROUBLESHOOTING
ENDS
Repeat procedure until troublefree operation is obtained.
NO
NO