Atwood Water Heater Problem.

I just started from fresh a couple of minutes ago. The burner stayed on for 22 minutes. Again, just a few seconds of luke warm water. Adjusted the temperature control to High, burner started and ran for 12 minutes. I got hot water for approx. 10 seconds, then war for a few seconds, then cold.

The heat generated for a total of 34 minutes has to be heating the water better than that?

There is no air in the lines. No anti-freeze by-pass. No check valve that I can see.

I'll add a photo of the plumbing with the various shut-offs - all of which I have on open.