Please Help! Rheem Hot water heater

[Glockandhammer]

To all:
I’m new here. Thanks for the help. I have a 3 year old 40 gallon RHEEM water heater. The issue I’m having is that the water runs hot for a short time and then goes cold. It’s most noticeable in the master bathroom which is two floors up and the last fixture in the chain. Here’s what I’ve tried so far.
1. Replaced dip tube. This was not the problem. No issue with the one I took out but replaced it anyway.
2. Replaced gas control unit. One company said this was the problem. It didn’t change anything. They said the burner might need to be replaced, but it’s on back order.
3. They recommended a recirculating pump. I read up on this. My problem is not the like warm water from the pipes has to drain out to the master and then I get hot water. I get the initial luke warm water and then about 2 mins of hot water and then back to luke warm.

For clarity- the water coming out of the hot water heater goes cold. You can barely touch the pipe when you first turn on the faucet. A very short time later, it goes cold at that pipe.

it’s like the hot water heater only holds 2 gallons or something. I can’t find a anti scalding valve anywhere. Any ideas???

 

[Twowaxhack]

Go to the water heater and turn the water off at the top of the heater with the shut off valve.

Go to a hot water faucet and bleed the pressure off......

The water should stop flowing at this point.

If the water doesn’t stop flowing, that means you have a cross connection between hot and cold.

This is when cold water flows into the hot and will cause temp problems like you’re having.

Try what I’ve suggested snd let us know what happens.

 

[breplum]

We've seen this symptom on recirc systems with bad Kohler K304 series shower valves and also old KWC shower valves.
Solution in those cases was replacing the pressure balancing cartridge assemblies aka the cartridge.

 

[Glockandhammer]

sorry for the delay. We were traveling over the holidays.

I tried what you suggested. Confirmed. There is a crossover. It ran slowly with the hot water supply off but valve open. Cold water. I shut off all the supply lines at each sink and toilet. That didn’t change anything. It has to be in either the shower valves or the tub. The tub is two handle. I have two Delta single handle faucets. My guess is it’s one of them. I read up on some other test and can hear water running on them when the cold supply is off and drained but the hot is on.
Best to just change them both out?

 

[Twowaxhack]

Single handle Pressure balanced Delta tub/shower faucets will flow a small amount of cold water when the hot water is turned off at the water heater.

That’s how it works.

 

[Twowaxhack]

Are you sure the cold water valve at the water heater is completely shutting down the hot water ? It should.

Turn the hot or cold off at the washing machine and recheck the problem.

 

[Glockandhammer]

First. Thanks so much for the help.

I tested using the kitchen sink. It’s the first in line after the water heater I think.

So I turned off the cold water at the hot water heater. These pipes and fittings are not old or in bad shape. Valve moves freely and I think it’s good.

I drained the hot water at that fixture. It took zero time. Lost pressure immediately. It ran a small amount of water consistently through this process.

I then shut off the supply lines at each fixture that I could including the washing machine. No change. I also shut the supply lines at the kitchen sink off and went to the bathroom and tried again. Same thing. Steady small flow.

I then went to the garden tub. Two handles. No change. I moved to the Delta shower mentioned above. Turning on the hot water caused the downstairs sink I was using to test to stop. Nothing came out but you could hear water in the fixture for a few seconds.

It seems like it’s isolated to those delta faucets, but can’t be sure.

I also have a Moen Flo so I can see if any water is moving in from the main of that helps at all.
Thanks again!

 

[Twowaxhack]

When you have a cross over, cold water will flow out of all the faucets through the hot side when the water is off to the water heater.

If that’s not happening then you don’t have a crossover.

 

[Twowaxhack]

Are you having trouble with temperature fluctuations at any other faucet other than the master shower ? What type shower faucet is it ? Delta single lever that turns on from right to left ?

 

[Twowaxhack]

Reading your first post again, it sounds like it’s a dip tube issue or your gas control is malfunctioning and not heating a full tank. You have stated you replaced the dip tube.

I’d do a draw test to see if the water heater was putting out the correct amount of hot water. A 40 gal heater will put out approximately 27 gallons of thermostat setting hot water before it starts to drop in temp.

So if your heater is set to 125 degrees you should get 27 gallons of 125 degree water then the temp should start dropping off.

 

[Twowaxhack]

I might would cut the hot pipe exiting the water heater to do this test considering your situation, you think you may have a crossover.

cutting the hot pipe at the water heater would eliminate any crossover possibility during the water heater draw test.

It would also verify a crossover if you have one. If you have a crossover the hot water pipe on the house side will never stop flowing water out of it.

 

[Glockandhammer]

I’ve done that test not at the water heater. I could try a faucet downstairs to see if I get a different result than when I did it upstairs. It’s really like a minute or two of hot and then lukewarm.

I can see the value of cutting the hot line going out. That way it just the water heater being tested not the rest of the system.

I had part of the gas control system replaced. The outside part with the knob. The other part is backordered. I think that was the burner.

 

[TomFOhio]

Fire the water heater up and watch the burner. See how long it runs. If your only getting about 2 gallons then it probably
shuts off early. If your getting a full tank of hot water then change your cartridges.