Suburbans have a bent interior pick up tube(mounted on the interior hot exit fitting) that KEEPS Hot water flowing without getting the diluted cold water intake. IF that tube is knocked loose, the cold water coming in the bottom as it mixes with the hot water will dilute to normal hot water that would exit at the top. Things that can dislodge this tube
1. Inserting a screwdriver into that hole to clean out or check for mineral or debris
2. Inserting a threaded fitting too far into that hole(very hard to do this)
3. Inserting a pressurized clean out wand/tool into the anode rod hole to powerflush the inside of the water heater.
I have only seen 3 or 4 of these over 41 years. It is NOT a servicable part as they do not sell that part. Once inside the tank it will just sit there.
NOW, if you are POSITIVE you do not have a Water Heater Bypass malfunction, then this pick up tube would be the likely problem. Doug
