Water Heater barely warm water - NO bypass valve

OK, so ran the WH for 30 minutes (never turned off on it's own), then popped the relief valve. Water that came out (caught it in a cup) was barely warm to the touch.

The flame is interesting. It's blue, with large flashes of yellow at the exit of the tube. At the entrance of the tube (near the jet) it's like a super-fast sputter, but blue.

Is it a thing for water to be in the gas line? If so, how do you purge it? (cooktop seems entirely normal)

Any other ideas?

Thanks!
Doug