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IF it was the sail or limit switch you would not get ignition.
The circuit board will not receive power until the sail switch is closed by adequate air flow from the blower. The power must also flow through the limit switch.
When the circuit board is triggered by this current, it delays ignition for about 15 seconds to allow the blower to purge the combustion chamber of any unburned gases.
The circuit board then sends high voltage pulses to the electrode assembly, providing a series of sparks to ignite the gas/air mixture.
To me it sounds like a control board or electrode issue if you are getting gas. Make sure the connections are good at the board. Make sure the ceramic on the electrode is not cracked or it can ground out.
Most shops do have a tester for that board, some charge a small fee and others do not...
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