I pulled the voltage selector and nothing looked burned or broken. I put it back in.
I pulled a few manifold bolts out one at a time and none had water.
L1 to L2 voltage is 240
I couldn't really get my probes into the S1/240 connector with it plugged in. I unplugged S1/240 and probed both the fenwal s1/240 terminal to S2, and the wire going to S1/240 to S2 and was getting some odd voltage like 17v. Maybe that's because of the non true-rms meter. Same thing for S1/120 to S2.
I also ran another test and checked that my breakers were working when my probe slipped off the L1 and shorted it to the chassis. Breaker is working!!
TH is 0 when heater and blower are off. When blower started, TH had about 26v. So I assume that's working. But like you say, it may be sticking or intermittent, so I'll replace it.
I ordered a Fenwal ignition module and air flow switch.