I have a Goodman GMS90904CXA thatwon't ignite. I switched my theromstat to heat and the vent fan came on but it did not ignite, I checked the unit and it was flashing 3 times(with vent fan running) I shut it down and did a startup procedure, same results.vent fan came on but did not light and still flashing 3 times, any help would be appreciated.

Look on the inside of front door/panel it should tell you what the 3 flashes mean

Thanks for the info I found a similar posting that said code 3 indicates a pressure switch.I pulled both tubes to check and found a Spider and nest in the one tube.Once I cleared it out and replaced it if fired right up.Thanks for the info I appreciate it.

Glad you got it going

Just found out the expensive way,same thing,fan but no heat and shuts off after a few.turned out to simply be a clogged vacumum line from the fan to the limit switch,clean out the nipple on the fan.cost me $196 to find out,hope this will save $$