Call for heat, Thermostat
contacts close
Does Yellow LED light for
approximately 2 seconds?
(Module Self Check)
yes
Does Yellow LED Flash?
no
Does Red LED Flash or remain
lit?
no
Does Green LED Light?
yes
Does Green LED Flash?
no
After prepurge does ignitor
glow red?
yes
Does the main burner light?
yes
Does system run until call for
heat ends?
Yes
Normal Operation
Check Low Voltage to module (TH-TR). If no voltage:
Check Limit Switches
no
Check vent pressure switch (if used).
Measure AC voltage between terminal L1 and TH. If voltage
is approximately 145 VAC, polarity is reversed; reverse
secondary leads on control transformer. Correct reading
yes
should be approximately 95 VAC.
Reset control to clear lockout and confirm fault.
Rapid Flash = Flame Sensed when no flame should be present.
1 Flash = Number of Retries exceeded, control locked out.
2 Flashes = Recycles Exceeded, control locked out.
yes
Red Light continuous indicates either an internal fault or
miswired gas valve. Check wires at MV1 and MV2 for proper
connection or swap wires to correct fault. If fault persists,
replace module.
Check Low Voltage to module (TH-TR).
no
Check Limit Switches
Check vent pressure switch (if used).
Indicates a poor flame sense signal. Check for short in Flame
Sensor wiring, Poor Furnace or Burner Ground, Shorting
yes
flame sensor, flame sensor wiring, or dirty flame probe.
Clean flame probe.
Confirm 120 Volts to ignitor terminals (HS1 and L2 on
no
module) If voltage is present replace ignitor.
Check gas supply and pressure to valve.
Check for 24 volt output on module (terminals MV1 and MV2).
no
If no voltage replace module.
If gas valve is receiving voltage but not opening replace valve.
Check limit switches.
no
Check sensor lead and ground for continuity.
Check insulator of flame sensor or ignitor for excessive
temperature. Temperature above 1000 deg F. can ground
flame sense.
TROUBLESHOOTING
5