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Kevin Thigpen

Technical Services Manager
North Alabama District

Ignition Proven Fault Code 6

An ignition fault is a common fault with a furnace and it could be caused by several things. For example, a standard Heil 80% AFUE furnace will try to light a total of 4 times before the furnace locks itself out on a “Code 6”.

This fault can happen during the beginning of a trial heating call or after the furnace lights if it loses flame sensing. If a furnace loses flame before the blower cycles on, the blower will run for the selected off-delay time it is set at on the control board.

Furnace Wire Diagram

If you have this fault, check the following:

  1. The green/yellow wire on the gas valve MUST be connected to the sheet metal cabinet to ensure there is a good ground to the control board and gas valve.
  2.  Make sure the gas shut-off valve is turned on completely and verify that the electronic gas valve is turned on also.
  3. Check the gas inlet and manifold pressure. A furnace with low pressure will have problems lighting from time to time due to under firing and can only light if other gas appliances are not on at the same time. Low inlet pressure can also be an issue due to the gas line not being large enough to supply the furnace with enough gas pressure. Check the line size to ensure you have a sufficiently sized line.
  4. The flame sensor is also an item that will need to be checked. You will need to check the micro amps. A normal reading will be between 4.0 to 6.0 micro amps. If there is oxide buildup on the flame sensor you can clean it with fine steel wool.
  5. Check the crossovers to ensure adequate flame crossover on the burners and clean if necessary. Rust or debris can will prevent the flame from reaching the flame sensor.

This should help you with checking various common issues so you will be able to find a reason why a furnace is locking out on a 6 fault. Remember to check your grounds first

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