Rapidly declining hot water

[drones]

I recently moved into a new home that has a 50 gallon water heater plus a hot water recirculator pump ( Grundfos UP 15-42F and a Honeywell aqua stat L6006C set for 130, 5 degree differential.

My problem is the hot water runs out way too early; about 10 minutes into a shower. The temp on the water heater for both the upper and lower are set to ~140 but the temp coming out of the nearest faucet starts at about 127 and rapidly goes down to ~99 in less than 7 minutes.

I think there is a crossover issue as I turned off the cold water supply to the water heater and turned on the hot water outlets in the bathrooms. The master shower runs when I turn on the hot water. Is this the cause of my running out of hot water?
Thanks for your help.

 

[Master Plumber Mark]

i would start with a new dip tube

 

[Sponsor]

 

[drones]

i would start with a new dip tube

I thought of that, but because the water heater is only 1.5 years old I dismissed it as probable. Still a viable possibility?

 

[Reach4]

If the WH is electric, maybe lower element has failed.

That does not address the cross-over symptom.

 

[drones]

If the WH is electric, maybe lower element has failed.

That does not address the cross-over symptom.

I checked both elements and thermostats. With all else equal, would the crossover issue cause what I am experiencing?

 

[Jadnashua]

A cross-over situation will significantly decrease the apparent hot water supply by diluting the hot.