I have a weathermaker 8000 58wav. It will startup, induction fan on, flames on, blower on for about 80 seconds. It then shuts down the flame and the induction motor. The blower will run for a short time and off. Blinks 31. Pressure switch was Ok, Flame sensor seems Ok. I checked the chimney vent at the roof and it appears clear. Any ideas??

31 is the pressure switch didn't close or reopened. This pressure switch is in your furnace to monitor the combustion fan motor to prove you have positive exhaust gas pressure out your exhaust vent and through your combustion chamber. This could be triggered due to plugged intake and/or exhaust piping, defective exhaust blower fan, excessive wind, plugged tubing on the pressure switch, etc. These pressure switches are very sensitive, do not take the hoses off and blow into the switch or you will damage it. I have also seen where an improper grade on the furnace will cause this fault. It should have a slope of about an 1/8 th of an inch from the back to the front of the unit, if not you may build up condensate in the secondary heat exchanger and not get enough flow through the ventor motor.

Both of these conditions can be reset by turning off the power to your furnace and then turning it back on. The furnace will then go through its normal start up procedure.

Have a look at your vents outside and make sure that there haven't been any birds taking up residence in your vent pipes, also check your condensate drain ine to make sure it isn't plugged.

Good luck, if in doubt get it checked out by a pro, this isn't a trade you want to mess with if you aren't comfortable

NOTE: exact Carrier wording

((pressure draft safeguard auxiliary limit or blocked vent shut off switch did not close or reopened))

the outside vent at the roof had some residue and I cleaned it out.I took the pressure switch out of the equation and it still functions the same way. I removed the vent at the furnace and cleaned it out, there was some residue in there. The old exhaust fan was bad and I replaced it with a new one.

Did your heat start working after you replaced the inducer motor or is it not working even after you replaced the motor? You can't remove the pressure switch from the equation the control board knows if its open or closed on startup if you try to jump it out it won't work the board is seeing it as stuck open.