Rheem 49 gal model #81V400 - hot water lasting only 5 minutes. What to do?

http://waterheatertimer.org/B220C.html
http://waterheatertimer.org/How-to-wire-water-heater-thermostats.html

Gene

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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.

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1) Rheem 81V40 electric water heater ... manufactured pre 2009 ... posted serial number does not match manufacturer
http://waterheatertimer.org/pdf/Find-Age-of-water-heater.pdf
http://waterheatertimer.org/pdf/Rheem-Ruud-2009-water-heater-parts-by-model-number.pdf page 5

2) Possible date of manufacture 11-1994

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

Ordinary tank-type electric water heaters are fully repairable by homeowner.

A) Basic info on Rheem
Rheem electric water heater website:
http://www.rheem.com/products/tank_water_heaters/electric_water_heaters/
Find age of Rheem: look 2nd and 3rd digit of serial number, for example 06 is 2006

B) Water heater has some hot water.
That says certain things: upper element is working, water heater electricity is working, reset button is not tripped, and heater is not experiencing run-away overheating event.
http://waterheatertimer.org/How-it-works.html

C) That leaves 4 suspects that cause lower amount of hot water.

1) TP valve is running hot water out of tank -or- leaking faucet is running hot water out of tank.
Check for leaks
http://waterheatertimer.org/How-to-replace-TP-valve.html

2) Lower element is burned out.
Test lower element using inexpensive multi-meter from Home Depot.
http://waterheatertimer.org/How-to-test-water-heater-element.html
Replace element with same wattage shown on label, and clean out sediment:
http://waterheatertimer.org/How-to-clean-sediment-out-of-electric-water-heater.html
http://waterheatertimer.org/Clean-sediment-out-of-water-heater.html

2) Upper or lower thermostat is bad.
Replace both thermostats for about $25.
http://waterheatertimer.org/How-to-replace-thermostat-on-electric-water-heater.html

3) Burned or shorted wire located between upper and lower sections of tank.
Turn off power. Open covers on side of tank. Remove insulation. Inspect parts for signs of high heat and burning. Especially check lower element. Tighten any loose wires. Replace part that shows signs of burning.
Put insulation and cover back over thermostats so cooler outside temperature doesn't cause thermostat to misread tank temperature.
http://waterheatertimer.org/How-to-troubleshoot-electric-problems-with-water-heater.html

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Also take advantage of fixya phone service.
For a price, expert speaks with you over phone while you work on water heater or any do-it-yourself project.
Fixya is always less expensive than a service call.

The tank has to be completely full of water before turning on electricity or elements will instantly burn out:
http://waterheatertimer.org/How-it-works.html

I would take 40 minutes and do complete troubleshoot before replacing anything else.
This requires $5 multimeter from home center.
Put battery in multimeter.
When testing voltage, rotate multimeter dial to 240-250-277VAC
When testing continuity and elements, rotate multimeter dial to Ohms
http://waterheatertimer.org/How-to-troubleshoot-electric-problems-with-water-heater.html

There are a lot of words on the page, but everything is simple and anybody can fix their own electric water heater.
After that, water heater is no longer a mystery and you can save money instead of ever calling service technician again.

Add a comment for more free help.
Also take advantage of fixya phone service.
For a price, expert speaks with you over phone while you work on water heater or any do-it-yourself project.
Fixya is always less expensive than a service call.

Rheem bolt-in element is 4500 watt.
Buy at hardware store or plumbing supply.

Hello Check the red overtemp reset button at the temp control.Check for contintuity at the elements with a volt meter (pull one wire off first) they should have a reading otherwise they are open & shot.Last is overdrawing (busted pipe) shut off the cold water supply for a 1/2 hour and open it back up and feel the hot water supply pipe.Is it hot?The tank can't keep up with the demand.

if your water heater is leaking from the tank, and not around any fitting, then you will need to replace the heater.
you can flush the heater, once a year is always recommended, however once every 2 years is sufficient.

scale, and deposites inside the tank will cause erosion and eventually eat through the walls of the tank. not much you can do to prevent this. the steel in the new tanks just don't last like they ued to.

I am afraid that you have burned the heating element out or an inline fuse is burned out

Take these steps, ensure you are recieving correct voltage to the heater. If this has been confirmed, then using an ohmmeter, with the power turned off, check the resistance through you heaters. You should read a resistance through the heater(s). If you read OL, it means the heater is broken, and if you read 0 the heater is shorted. Hope this helps