Hi lcottrell, I did notice earlier that you had tested the elements and had replaced both the elements and the thermostat. But you need to really verify, at least, that there is voltage to the elements when there should be and ideally that there is current flowing through the element circuit. A successful current test would rule out a lot of electrical issues. An ohm test on the element only tells you that the element is good-- it doesn't tell you if it is getting power. Unless I am forgetting something, there is either an electrical problem, a mechanical problem with the thermostat, or you are using all of the hot water in the tank (which would include a low setting on the thermostat or diminished tank capacity due to lime buildup). If you had serious lime buildup you would have known it when you pulled the bottom element. Less likely but still possible is a tank that has been connected to water supply incorrectly (the cold is connected to the "H" outlet on the top of the tank) or the dip tube is damaged or missing causing cold water to mix with the hot in the tank. Of those two, the improperly connected plumbing doesn't fit your symptoms, but the damaged dip tube does. Since the electrical is the most likely problem, you need to conclusively rule that out before you do anything else. I am sorry if it sounds like I am telling you to recheck something that you have done already-- but if you are stuck, then you need to perform some conclusive tests.

Look at the cost benefit of going tankless, the cost will be much higher and payback may be years coming. May need a larger gas line, will need a new vent stack, etc. For the two of us the cost for tankless was not justified. I installed a 50 Gallon Bradford White, the tank cost was approximately $400. Normally with labor in the area it costs around $800 to install. Power vents not normally used where I reside. Guess with power vent cost to install $1000 assuming electrical is near. Tankless quotes here are between $3000 to $4000. Most gas lines need to be changed to accommodate gas volume requirements and the vent needs to be changed to handle the increased heat. Not a fan of Sears or their water heaters, Bradford White was rated the best by Consumers Reports. I am very satisfied with Bradford White. Looks like turning on and off reset the blower. My two cents.

I had a conversation with a local pro, and he believes adding a mixing valve and turning the aquastat up from 100* to something like 140* will do wonders. He said it's normal in any water heater to have much higher temps at the top and lower at the bottom, with the average around the aquastat setting, meaning we have ours turned way down. I'll give that a try. On the DHW priority wiring, I'm having a little difficulty finding straightforward info. Most diagrams/discussions include so many references to controllers and various models of components that I can't tell what the basic schematic should be. Here is my current setup:We have a single circ pump controlled by the boiler control. I just learned that the "DHW End Switch" terminal in my boiler goes to the HydroStat controller and only bypasses the thermal targeting in order to get full power from the boiler during DHW demand. My plan now is to simply add a DPDT relay (in red below) with the coil powered by the aquastat, that disconnects the signal to the two heating zone valves from their thermostats. This will will close those valves while the DHW is heating and create the priority setup. Anyone see any problems with this setup?

@Karen Williams This is the control panel on my tankless water heater. Water Set Point ... the output temperature the unit feeds into the hot faucets ... can be set in 1°F increments between 50°F and 140°F. Temp Up and Temp Down buttons adjust the Water Set Point temperature. Then press Temp Set to make it the normal at-all-times temperature if desired ... otherwise the adjustment is temporary and will revert back after a number of minutes. I have 103°F as the "normal" temperature and raise it when needed for washing dishes or clothes, without pressing Temp Set, and it reverts back to 103°F after 30 minutes so I don't have to remember to do that. That's just how my unit works, they're not all the same. Setting the temperature "at the faucet" means I set the water heater to the temperature of heated water I want/need "at the faucet" ... such as 103°F for a shower, instead of 120°F or 135°F which is much hotter than needed for a shower ... and I turn on only the hot faucet (or set a single-lever faucet to full-hot with no cold mixed-in). Thus, the tankless unit has a high-enough flow rate passing through it for the duration of the shower to insure it doesn't shut off due to too-low flow. 120°F, 135°F, 140°F output temperature requires mixing in cold water and turning down the hot flow at the faucet to get a comfortable shower, which reduces the flow through tankless possibly below the required rate which can cause it to shut off completely and the shower goes cold. Remote control panel means exactly that ... some tankless water heaters can have an optional extra temperature control panel installed at a convenient location such as bathroom or kitchen so the homeowner doesn't have to go down to a basement or out to a garage or wherever the heater is located to adjust the temperature. My heater doesn't have a remote control but it's located in a broom closet in my laundry room behind the kitchen near the center of the house so is easy to access any time I want to change the setting.