I recently replaced my old Kenmore PowerMiser 9 with a new version of the same model. My wife likes to take steaming hot baths, so she is used to running full hot water into the tub until it runs out, and then she takes a half hour to ease herself into the water. Strange, but true. Since we got the new heater, though, she can only run a few inches of hot, then it gets lukewarm. The water gets plenty hot, and the recovery is pretty quick, so it seems like the burner is doing its job. There is plenty of hot water for long showers, but of course the water is blended hot and cold.
So, I reasoned that the problem was a faulty inlet tube that was allowing the cold water to mix with the hot too high in the tank. The original tube looked fine, but I replaced it anyway. This is the new RotoSwirl tube that is supposed to swirl cold water around the bottom of the tank to keep it clear of settlement. My latest theory, then, is that this swirling is what is mixing the cold with the hot too high in the tank, and if I cut off the end of the tube it will give my wife the hot bath she wants.
Any thoughts/suggestions/warnings other than "tell your wife to take a shower?" I tried that already.
Make sure the inlet of the WH is connected to the cold supply. Is the thermostat set on the high side? Where I live, they require a tempering valve to ensure the outlet won't scald you, and you would not be able to get water that hot unless you defeated it, regardless of the WH thermostat setting.
If you can get her to run the water just when she wants to enter the bath, you'll have a better chance since then, it'd be filling with the tempered water, and you'd be able to get more.
Important note - I'm not a pro
Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013