Electric water heater problem

[Jamco70]

1. Started getting warm water instead of hot water from 7 year old Rheem electric water heater set to 120 degrees.

2. After research, I replaced both elements.

3. When I turned the power back on, the water heater immediately threw a "Lower thermistor failure" code.

4. Rheem no longer makes this particular thermistor and I did not want to wait 2 weeks to get it from Home Depot by mail.

5. Replaced water heater with brand new Rheem water heater. Set one thermostat to 120 and the other to 125, according to manual.

6. Experiencing same problem....have to turn temperature control all the way on Hot to get warm water in shower, kitchen faucet, and master bath faucet. The water coming out of the relief valve is 118 degrees.

7. Did some research, someone suggested it is a bad mixing valve in the kitchen sink faucet????

I have never heard of such a thing. Is this possible?

Side note: we are remodeling the master bath and the contractor replaced the cartridge in the Moen shower body and capped the shower arm until the shower tiling is done. I looked at the cartridge today and saw that it was left in the "notch up" position. I turned it to the down position. Could this have been the culprit?

 

[Sylvan]

Older Moen shower valves had bypass problems . Possibly you have that type

 

[Sponsor]

 

[WorthFlorida]

Not sure what your are referring but the easiest way is at all sinks and laundry, turn off the cold water stop valve. Sometimes there is no way to shut off the shower or tub. Run the hot water one at a time. If everything is hot, then open one cold water valve at a time and check the water temperature.

 

[Terry]

Notch should be down. That was it.
You had a capped nipple at the shower head location with the water full on. it allowed water to pass through.
Turning the valve off, notch down will fix that crossover.