Combustion Probes

• The combustion probes contain 3 prongs: blue wire is the flame rod sensor and the thicker black wires are the ignition probes
• Meters (multimeter)
  • Checking voltage at spark condition, visual check in sight glass window
  • Amp draw on flame rod test
• Removing it <video>
  • Cleaning up and putting back together

You need air, spark, and gas to achieve combustion. When the heater starts operation, you can clearly hear the fan motor ramp up. Gas pressure can be verified with a gas manometer and the spark at the combustion probes.

There is a gap between the probes to provide the space for the spark to jump to the burner plate, meeting with air and gas to ignite the burner.

If the probes become caked with debris, then it can be wiped clean with a scouring pad or paper currency. However, the debris build-up indicates abnormal combustion potentially insufficient combustion air, block exhaust, or high gas pressure supply.

The flame visible in the sight glass window should burn blue. If the majority of flame is yellow, orange, or red, then that indicates less than ideal combustion conditions. Verify gas pressure, clean air supply, an exhaust free from obstruction, and the dipswitch settings.