I am working on a Ruhd 90+ 60,000 BTU furance. It fires up then shuts down after awhile it will go into lockout. I cleaned the flame sensor and it fixed it for a day then lockout so I put a new flame sensor in and it fires up good for a day then lockout. Checked drain pipes all clear vac switches look like they are working,intake and exhaust pipe look good.After reset all works for a day. Not sure what I am missing could it be the induction fan is failing but vac switches move as soon as fan startes? Of course when I go to check any problem the furance fires and run like it should.

If its locking out you should have a code on the control board. A semi restricted drain can fill up with water, open the pressure switch only to drain down over time. Yes I know it's a stab in the dark but its something to check. Did you check the gas pressure and clean the burners?