What is the most likely cause of this inducer motor comes on but unit won't ignite model #pgaa36d1k3

Typical operating sequence (some slight variations of timing are likely): 1) Inducer starts and pressure switch engages, 20-35 seconds. 2) First ignition trial begins, ignitor is powered and glows, 17-34 seconds. 3) Gas control is powered and main burners ignite, furnace pre-heats, 20-35 seconds. 4) Blower starts and runs for duration of heating cycle. Compare this to what you observe (eyes and ears) and post back. Also, look for a blinking diagnostic LED.

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Originally Posted by KC13

Typical operating sequence (some slight variations of timing are likely): 1) Inducer starts and pressure switch engages, 20-35 seconds. 2) First ignition trial begins, ignitor is powered and glows, 17-34 seconds. 3) Gas control is powered and main burners ignite, furnace pre-heats, 20-35 seconds. 4) Blower starts and runs for duration of heating cycle. Compare this to what you observe (eyes and ears) and post back. Also, look for a blinking diagnostic LED.

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Does not have led light we replaced the gas valve that was not it replaced rollout switch nope not that either replaced control board now nothing there were serveral burnt spots on the board could the pressure switch be the problem since the inducer motor was coming on before and now its not

The burned spots indicate a problem with the old board, but if you have less operation now than before, double-check the board wiring before the Magic Smoke is released from it. Once it escapes, it can't be put back, and another board will be on the to-do list. The pressure switch may have been the problem before, and the parts you have replaced already may not have been the problem at all.

Quote:

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Originally Posted by KC13

The burned spots indicate a problem with the old board, but if you have less operation now than before, double-check the board wiring before the Magic Smoke is released from it. Once it escapes, it can't be put back, and another board will be on the to-do list. The pressure switch may have been the problem before, and the parts you have replaced already may not have been the problem at all.

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It was wired the same way it came off I done them one at a time if that pressure switch is bad would it cause it to have less operation after replacing the board then it had before the board was replaced

Check the installation instructions for the board. Unless it is an exact replacement for the original, there may be additional steps that must be followed for it to function correctly. I would not expect a faulty pressure switch to cause less operation than before, but if the new board has safety features that the old one lacked, it is possible, if the pressure switch is stuck in the engaged position. Try this: pull the wire off the C terminal of the pressure switch. Does anything happen?

Quote:

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Originally Posted by KC13

Check the installation instructions for the board. Unless it is an exact replacement for the original, there may be additional steps that must be followed for it to function correctly. I would not expect a faulty pressure switch to cause less operation than before, but if the new board has safety features that the old one lacked, it is possible, if the pressure switch is stuck in the engaged position. Try this: pull the wire off the C terminal of the pressure switch. Does anything happen?

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OK before reading yours I put uld board back on inducer motor came on so your righ about the board is there any way to check pressure switch or jumper it

You will need a multimeter. Set meter to check ohms/resistance, disconnect wires from pressure switch. With inducer off, you should read infinite resistance through switch. With inducer running, you should read 0 resistance through switch.

Quote:

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Originally Posted by KC13

You will need a multimeter. Set meter to check ohms/resistance, disconnect wires from pressure switch. With inducer off, you should read infinite resistance through switch. With inducer running, you should read 0 resistance through switch.

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Thanks for all your help. You know what it ended up being? t-stat.guess I should have been thinking more simple lol.