Frequently Asked Questions


  1. What do the different flash codes mean?


  2. What Causes a Soft Lockout Condition?


  3. What will cause a furnace not to sense flame?


  4. Why does the Induced Draft Blower and main blower run but the furnace will not go into the ignition sequence?


  5. What will cause the main limit to open?


  6. What will cause the roll out switch to open?


  7. What will cause the pressure switch to open?


  8. Why does the 80+ and 90+ gas furnace use different LP kits?


  9. What causes the furnace to go into a soft lock out when flame signal and flame signal light dose not indicate low flame signal?


  1. What do the different flash codes mean?

    • 1 Blink - This is a soft lockout condition.
      • No Flame Sense was detected after four ignition trials.
      • Four flame failures during one call for heat.
      • Turn off the 115 volt power supply to the furnace or turn the thermostat off for 5 - 10 seconds to reset the soft lockout.
    • 2 Blink - Negative Pressure Switch Circuit is open.
      • With a MAGNEHELIC GAUGE check to verify the negative pressure from the Induced Draft Blower is at least 0.1" beyond the Switch closing setting.
      • Check for blocked pressure switch tube port on the Induced Draft Blower housing.
      • Check for blocked or restricted vent pipe
    • 3 Blink - Limit Control Circuit is open.
      • The main high limit control may be open due to low air flow or a over fired heat exchanger.
      • The manual reset rollout switch located above the burner may be tripped. Check for excessive manifold pressure. Check for blocked flue or heat exchanger.
    • 4 Blink - Pressure Switch is closed.
      • The switch contacts remain closed during the off cycle. The points may have welded together or have become stuck. The furnace will not go into the ignition sequence if the pressure switch does not open from previous call for heat.
    • 5 Blink - Twinning Fault.
      • Check to make sure there is not a thermostat wire connected to the twin terminal of the Integrated Furnace Control.
      • Check the control board switch setting and make sure the switch is set correctly for the application.
      • If two furnaces are twinned make the Integrated Furnace Control in both furnaces are the same. If the boards are not the same they will not operate together.
      • Some times a twinning fault can be caused by the thermostat or faulty thermostat wiring. To check for this condition remove the thermostat wires from the Integrated Furnace Control and use a jumper from R to W to see if the fault code goes away.
  1. What Causes a Soft Lockout Condition?

    • No Flame Sense was detected after four ignition trials.
    • Four flame failures during one call for heat.
    • Turn off the 115 volt power supply to the furnace or turn the thermostat off for 5 - 10 seconds to reset the soft lockout.
  1. What will cause a furnace not to sense flame?

    • One cause of failed flame sense is improper phasing or polarity
      • With a volt meter read the voltage between L1 and the Neutral terminal of the Integrated Furnace Control. The voltage should be 115 volt.
      • With a volt meter read the voltage between L1 and the cabinet equipment ground. The voltage should be 115 volt.
      • With a volt meter read the voltage between the Neutral cabinet equipment ground. The voltage should be 0 volt.
      • With a volt meter read the voltage between L1 and the "R" terminal of the Integrated Furnace Control. The voltage should be 96 volt. If the voltage is 144 volts the transformer is out of phase and the 24 VAC and the 24 Com wire on the Integrated Furnace Control should be reversed
    • If the Phasing and Polarity are correct the main cause for failed flame sense is poor or no equipment ground. Make sure you have a hard wired equipment ground from the furnace back to the load center.
    • Incorrect Manifold Gas Pressure can cause the failed flame sense
    • A dirty flame sense rod can prevent flame rectification.
  1. Why does the Induced Draft Blower and main blower run but the furnace will not go into the ignition sequence?

    • This condition occurs when there is an open in the limit control circuit of the furnace.
    • This condition can be caused by a poor terminal connection at the switch.
    • This could be a tripped rollout switch.
    • This could be caused by an open high limit switch.
  1. What will cause the main limit to open?

    • An open High Limit Switch could be caused by low air flow across the heat exchanger causing it to overheat.
    • Excessive manifold gas pressure can cause the heat exchanger to overheat and cause the Main Limit control to open.
  1. What will cause the roll out switch to open?

    • A lack of combustion air can cause the roll out switch to trip
    • A blocked Heat Exchanger and or vent can cause the roll out switch to trip.
    • A damaged Heat Exchanger can cause the roll out switch to trip
  1. What will cause the pressure switch to open?

    • The Induced Draft Blower not running to speed can cause a switch not close.
    • A blocked vent can prevent the Pressure switch from closing.
    • A damaged heat exchanger can prevent the Pressure switch from closing.
    • A crack or hole in the heat exchanger tube can prevent the pressure switch from closing.
  1. Why does the 80+ and 90+ gas furnace use different LP kits?

    • Each Inshot burner on a 80+ gas furnace has a fire rate of 25,000 BTU per burner. Each Inshot burner on a 90+ gas furnace has a fire rate of 15,000 BTU per burner. Because of the difference in firing rates the 80+ and 90+ furnaces require different orifices.
  1. What causes the furnace to go into a soft lock out when flame signal and flame signal light dose not indicate low flame signal?

    • On the up flow 90+ furnace the blocked drain switch is electrically in series with the gas valve. If the furnace has a draining issue the switch opens and de-energizes the gas valve. If this happens four times in a single heating call, the furnace will lock out on flame failure.


    • Field clues that this may be happening are that the equipment owner only sees this happen after long run cycles (conditions outside are close to design--- VERY COLD) or after t-stat set back recovery. Drain system should be inspected and cleaned as necessary. The condensation trap is a likely place for trash to accumulate and should be replaced or thoroughly cleaned while held upside down.

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