Edit: Wrote this before i saw your post above (5:45) You may want to read the next post first.
r4 is good, it's the firmware revision, and not a trouble code.
Did the HLS light come on for the tech.? And if it did, what happened when he jumped the high limit switch (HLS)?
Did the guy confirm the HLS was closed?
Dumb question: You mentioned that you replaced 3 items. Were these all new, out of the package? Or flea market/E-bay?
I would say, if you can find the two pins that connect the HLS to the main board, jump them, and the light stays on, it's the board.
Before you do this test, make sure to disconnect power from the heater (best way is at the breaker), locate and jump pins, turn on breaker, and give heater a call for heat. If the blower starts, there is a disconnect between those two pins (wiring and or HLS switch).
Buy a new $2000+ heater, or a $300 board? Hmm... How old is that one?