The inducer fan blows but I get a diagnostic code 31 that keeps the burner off. The pressure sensor switch isn't the problem (I have tried replacing it); disconnecting the hoses to it will allow the burner to fire. I can also uncap the internal inducer fan intake and get it to fire. My furnace guy gave up on getting it to work and told me to just leave that cap off so it could get plenty of air. I have checked that the inflow and outflow vents are unobstructed. I had the same problem last year, but the tech was able to get things adjusted so it would work (and there had been no problem in previous years). This year he threw up his hands and left. Does the auxiliary intake need to be capped? Any tips would be appreciated.
Try another furnace guy. I don't suggest poking around with the controls on a furnace unless you know exactly what they all do and why.
Start by contacting your local Payne factory representative. If your furnace guy is good (which i find hard to believe, since he has you running this equipment in a modified manner) and this thing is this fiddly, get the manufacturer in on the problem and quit poking it with a stick.
The furnace you are working with is a good furnace, this particular furnace is equivalent to the Carrier 58 MXA. What is the serial # on the furnace. When you are removin the cap is the one below the burner box or is it the one on the inducer? The other thing I need to know to help you is the product #. I also need to know what size of pvc pipe is on this unit, how many 90 deg and 45 deg elbows. If unit is only a couple of years old they may have not followed the venting guide. If you will let me know, I will help you fix this.