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Troubleshooting an Electronic Ignition Furnace

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Troubleshooting an Intermittent Pilot Ignition System

PROBLEM:
No Spark and Furnace Does Not Work

Possible Solution:

  • No power to furnace
  • Thermostat not calling for heat
  • Loose connections to/from control module
  • Damaged spark electrode
  • Faulty pilot burner
  • Faulty control module

PROBLEM:
Spark is Present, but Pilot Does Not Light

Possible Solution:

  • Loose pilot valve wiring
  • Pilot gas line bent or obstructed
  • Pilot orifice plugged; check and clean orifice
  • Faulty pilot gas valve
  • Faulty pilot burner
  • Faulty control module

PROBLEM:
Pilot Lights, but Main Burner Does Not Come On

Possible Solution:

  • Check that sensor cable and high voltage cable are separated
  • Faulty pilot gas valve
  • Faulty pilot burner
  • Faulty pressure switch
  • Faulty high temperature limit switch
  • Hose from pressure switch is loose
  • Faulty control module

PROBLEM:
Burners ignite then turn off after a few seconds

Possible Solution:

  • This can be a tricky one where the problem lies in a bad ground or the the black and white wires (neutral and common wires) being reversed (reversed polarity) in either the junction box or outlet powering the furnace.
  • The electronic ignition control module must ensure current flow through the flame sensor to ground and if the polarity is reversed in the circuit there is no voltage potential and the flame sensor does not work. So although the burners initially ignite the ignition control module will close the gas valve because of failure in the flame-proving (flame sensor) circuit.
  • If the black and white wires are connected correctly and the flame still drops out, then the issue may be a bad ground. Using a volt-ohm meter, measure between the white wire (neutral) and the green wire (ground) to be sure you have no voltage.
  • If this does not work, replace the flame sensor. See the tutorial Replacing an Electronic Flame Sensor.

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