Shower takes too long to get hot then runs lukewarm then hot lukewarm then gets cooler & and cooler &cold

get the installer people back to set the operation correctly as it should have been test run before they left
read your operators manual for settings or trouble shooting

Check by-pass valve(s) position on back of tank.

You could start by seeing if the thermostat is wide open. Sounds like it is on low or vacay mode. How far is the run between your heater and the bathing area. Might need to insualet some piping.

If you need further help, reach me via phone at https://www.6ya.com/expert/dan_73bbd84fe1d95b61

sounds like the mixing valve needs replacing

Try running the hot water in the sink while you have the shower. If the water in the shower stays hot, then the problem is not enough flow through the water heater to keep the heater running. I am guessing that the master bath is further away from the water heater than the guest bath. If not I would check the shower nozzle in the master bath to see if it is clogged a bit or if it is a water saver nozzle because this will slow down the water volume and then cause the water heater to shut off the heat.

If the water is only cool in the shower, it could be the shower valve. However if water is cool at all taps, something is not working on the water heater system.
Gary

Paragon 8145-20 is a 240V defrost timer
It is probably not best choice for water heater timer
Timer initiates defrost cycles each 4 hours.

A water heater timer should have more scheduling options.
-For example estimates show average run-time for water heater is 3 hours per day, depending on incoming water temperature, thermostat setting, and number of gallons used.
-To save money using water heater timer, you have to schedule times carefully so water heater runs less than 3 hours per day.
-Now your average electric water heater heats about 20 gallons per hour.
-Average shower uses 4-9 gallons hot water, so water heater needs to run 15-30 minutes (15 summer, 30 winter)
-Average bath uses 12-15 gallons hot water so water heater runs 45-60 minutes
-But lets say you run water heater for 1 hour and make 20 gallons of hot water. Then you take a shower, expecting hot water to remain in tank.
-Here's the problem ... cold water entered the tank to replace the shower water ... and the new cold water is cooling the rest of the tank.
-So a timer means scheduling hot water to match shower and bath events. For example taking shower and bath in immediate succession.
-Or set the timer for each individual hot water event ... for example set timer for 1/2 hour for shower, and later timer turns on 1 hour for bath, or 1-1/2 hr for 2 baths, etc
-> The flexible programming described above is not a characteristic of defrost timers.
I suggest Intermatic WH-31 240V or Intermatic T-104 240V or GE 15207. These are mechanical repeat-24 hour timers with manual override where each day has same schedule.
Digital programmable timers like Intermatic EH40 offer 7-day, 40 event programming. Weekends and weekdays can be different.
To see several box-type timers:
http://waterheatertimer.org/Boxtype.html

sometimes there are orings or gaskets that get tore in assembly one of those may be bad,or if it is around the threds you might try wraping teflon tape around the thred once or twice.hope this helps

Unit needs a new "dip tube" It is cracked and allowing cold in water to mix with all hot water resulting in "lukewarm water". Need plumbing skills to change out at cold inlet top of heater,pull out old,buy new at hdepot 5.99 reinstall.

Please rate Thanks

jj505

mixing valve must be replaced