OP stated:
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.
Water heater has water in it....so not bypassed
Water in WH was warm......after 30 mins
Cold/hot have to mix to cause 'warm'---OP took sample from T&P Relief Valve
OP stated:
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.
Flame is fuel rich so flame temp not as hot as it should be plus gas flow is not consistent ---dirty orifice and/or burner tube
OP also didn't let WH operate until heating cycle finished
