50 Gallon GPVT-50L 50,000 BTU ProLine XE Power Vent Residential Gas Water Heater w/ Side Connections - Tall (NG)

First word about the supplyhouse.com I purchased the water heater online with ease. Delivery was fast and right to my door and the price was the best that I was able to find. I installed the water heater on the day that it arrived without issue I was replacing a 25 year old A O Smith PowerShot water heater. This unit stands about 2 inches taller than the powershot, however the gas line enters at the same height which made installation fairly simple. The old powershot had so much scale buildup that it was no long getting the water hot enough. And I figured rather than mess around with a 25 year old water heater I may as well replace it. The new unit works great it's nice to have hot water again vs just warm water.

OK. SupplyHouse was great. Easy to install. The GPVT-50 has a more powerful fan than my previous GE unit & needed the plastic plate termination to provide some exhaust back pressure as my 3" pvc exhaust equivalent length is below 50'. This unit is much quieter than my previous gas powervent water heater. I am having a hard time getting the thermostat set to operate at the temperature I would like it to (or possibly it is not functioning properly?). I would like a "faucet full hot" temperature of about ~120 degF, good for the dishwasher and not so hot that I can't keep my hands immersed in order to wash hands or pots & pans. At this time, the GPVT-50 tends to run either "scalding", i.e., I have to pull my hands out (~130+ degF), or too low and does not reignite when I wish it would (I know by the screams of "where is the hot water?"). The initial recommended "HOT" thermostat setting was nominally to be about 120 degF but instead yielded 140 degF. Way too hot, burns. The "LOW" setting (nominally 110 degF) is giving the about 130 degF...still too hot. I am trying to get operation just slightly below this, but the knob control is analog and appears to be sensitive (assuming thermostat is working properly). There is one more unmarked dot below the LOW set mark, and then there is the VACation mark which is meant to prevent freezing and is nominally a 70 degF set point. These marks are equally angularly spaced, but not equally spaced by degreesF (delta 40 degF from LOW to VAC). BTW, the manual indicates that a number of short(?) hot water demands can cause the water temperature to go up as much as 20 degF ABOVE your high temp set point (page 41). Also, contact with AO Smith informs me that the difference between the high set temp and the the low reignition temp can also be 20 degF. So how do you set this monster, or determine if it is operating properly? IDK. May have to plumb in a cold water mixing valve...which wastes energy! Needs a digital thermostat!