Hot water decreases flow after 5 minutes (electrical)

[fcmack]

I had a new electrical water heater (Rheem) installed in our apartment - before it was inside the closet, but now we installed in the basement of the building. Due to the new layout, the main hot line is connected to a different point, near the laundry shut off. The old heater tank connection is closed now.
After this change, we have hot water in the shower but only lasts for 4 or 5 minutes, then warm, then cold. The bathroom faucet, same thing. However the faucet in the kitchen is working well, so we know there is no issue with the heater tank. It is brand new and it is 40 gallons. Model Rheem Performance 40 Gal. Medium 6 Year 4500/4500- Watt Elements Electric Tank Water Heater.

Why is that the hot water only lasts for a few minutes? There is no leaks anywhere in the building, no one is getting hot instead of cold water so I am assuming the connections are correct, the temperature setting in the tank is 140 oF. Could it be a pressure issue? I don't believe there is a need to have a pressure vent on a hot water line.

I tried to make a drawing on the connections with the new installations but I am not sure what is inside the walls, I can see the new hot water line coming in as the drawings, but I can't see what happens with the pipes just before the bathroom.

Any ideas?

Drawings: I will try to post on another box

Thank you!

 

[fcmack]

This is the schematic drawings

 

[Chuck]

Have you got the hot water and cold water connections to the Rheem unit the correct way round (i.e. not swapped) ?

 

[ShaunCorbs]

Have you tried after it goes cold running it opening the bathroom hot sink tap for a few minutes more eg 3-5 mins to see if it gets hot again ?

 

[fcmack]

Have you got the hot water and cold water connections to the Rheem unit the correct way round (i.e. not swapped) ?

I believe so, the install was done by a professional plumber and we tried the hot/cold taps and it worked normally.

 

[fcmack]

Have you tried after it goes cold running it opening the bathroom hot sink tap for a few minutes more eg 3-5 mins to see if it gets hot again ?

I will try that. Thanks!!

 

[Chuck]

I believe so, the install was done by a professional plumber and we tried the hot/cold taps and it worked normally.

That's not what I meant. Are the hot and cold pipes actually connected to the ports on the cylinder labelled 'hot / outlet' and 'cold / inlet' respectively?

The fact the cylinder was installed by a 'professional plumber' means it's unlikely to be wrong but it's easy to check. Everybody has their off-days and your pro has, after all, left you with a non-working system.