Why does my furnace high limit switch keep opening?

What people tried

Every workaround mentioned in the threads below. We haven’t tested any of them — and nobody here is claiming they worked.

1. 1
   Replacing various parts using a trial-and-error approach
2. 2
   Lowering gas pressure and adjusting blower motor speed
3. 3
   Consulting online communities for diagnostic ideas
4. 4
   Running extension cords directly from the truck instead of using the home transfer switch.

In their words

Unedited, grouped by where they were said, most upvoted first within each place, each linked to the thread it came from.