I have tenants who complained of rusty water, so I replaced the water heater. The amount of hot water they had was not an issue, just the rust showing up.

We replaced and installed the same type of heater - Rheem 50 gallon short, electric. The new heater only ran hot for a few minutes and then cold.

Plumber came back and turned up the thermostat, checked the elements and thermostat, and this did not resolve the issue.

Plumber came back and replaced the elements and thermostats, and replaced the dip tube. This did not resolve the issue.

Plumber came back and installed an entirely new water heater again. We let it heat for 45 minutes. It gave only 15 gallons of hot water before turning cold. (Looked to be same as other times, but first time I had measured with a bucket.) Plumber researched and said full tank of cold water heats at 22 gallons per hour. So we let it heat overnight, over 12 hours.

This morning, same thing. Few minutes of hot, and then cold.

How can this be with two brand new water heaters, and three dip tubes, elements and thermostats? Could something have happened when they installed it? They are completely out of ideas. Because it didn't have the problem with the old water heater, there MUST be an explanation with the installation?

Your complaint gives the classic signs of a failed dip tube, You could replace dip tubes all day long if you applied heat to the cold water inlet as you were connecting the cold water feed. A dip tube's secured by a plastic flange and if you apply heat to the cold water inlet the flange melts and the tube falls to the bottom of the tank,(see image). Let me tell you what happens when the dip tube's missing. A dip tube directs the incoming cold water to the bottom of the tank where it's heated by the loweand element and raises to the top where the upper element maintains the heat. If the dip tube's missing then the cold water remains on top where it mixes with the hot water and you run out of hot water in a hurry. There just isn't any other explanatio. Did you see the old dip tube the plumber replaced in the first heater? You could replace new water heaters all day long and unless you installed a 3/4" brass nipple on the cold water inlet you would still end up with the same problem.
Your plumber's not going to like me very much but on my opinion your problems were caused by faulty installation. Good luck. Tom

Hi Lilyhaca

A little far-fetched here, but how about checking the electrical voltage at both lines coming into the water heater? You should have a full 110-120 volt at each leg (making 220-240 volt total). Here, the electrical breaker/fuses may have malfunctioned back at the electrical panel (or subpanel) as a result of the plumber turning the breaker off and then on again at the end of the job. It would NOT be his fault is the breaker/fuse malfunctioned by the way (it would just make him a chump for not checking voltage before replacing the new heater with another new heater is all)... ;)

Let us know what you find, OK?

Mark

Just one more thing to check. Make sure the hot and cold are piped correctly. Say the original tank was installed with hot and cold on the wrong side, so the installer switched the dip tube to the hot side (which would now be the cold inlet side). Now comes along another plumber years later and installs a water heater like he is used to doing, but this means the cold inlet is coming in the hot side and the dip tube is still on the cold side. I agree with tom that it may be a dip tube problem, and this is just one other explanation of what could cause this. Every great once in a while we will come across a heater that was installed incorrectly years ago, and with very tight spaces to work with, find it is easier to swap the dip tube from cold to hot, but we always mark the water heater for future reference. Have your plumber double check this and make sure cold and hot are connected accordingly.

Hi - well I am now on water heater number 4. All dip tubes have checked out fine, all thermostats and elements have checked out fine. I have seen each dip tube, no holes, cracks etc, and were installed correctly. I had an electrician verify the wattage/amps. We have also checked that hot and cold were not crossed. Two different plumbing companies, and the Rheem wholesaler and Rhem rep cannot figure it out.

Just for my sanity, as I'm reading different things and can't find a clear answer: On a 50 gallon tank, how many gallons should I expect to draw before the temperature drops 20 degrees? I read that you should get 75% of the capacity of the heater in hot water, but that is so subjective. I need to know what is considered a correctly functioning water heater, at what points the water is expected to drop by 10 degrees and 20 degrees? Thanks!

There really is no set answer here. It all depends on how much hot water you are using, the actuall temp of incominig water (which varies greatly from climate to climate). On average I would guess you should get about 35 gallons of hot hot water, then it will become just hot at about 40 gal, then it will quickly become just warm, then soon after, cold. I know hot hot, then hot, then warm, then cold is not really giving any actuall temps, but that all also depends on what the heater thermostat is set on.

Now, are you experiencing a lack of hot water in all fixtures, or just , say for instance, a tub or shower? It may be time to look into other aspects of the pluming, like faulty fuacet cartridges (possibly a recirct line?) etc.

In my opinion, the only other way you could have the problems you are having is if you have a CROSS CONNECTION somewhere in the house.

Here, you may have a single handle valve with a mixing cartridge that has failed.

Heck, I've even had a really old two handle faucet that was tied together out of the faucet using a wye fitting with a shutoff and that was causing a new 50 gallon heater to have the same problem as you describe. Here, the cold water flowed across the wye and into the hot water supply and mixed with the hot water going to the nearest fixture... drove me nuts for an hour or so until I figured it out!

Have your plumber check for cross connections. Have him also isolate the washing machine solenoid valve (just shut off shutoffs to the washing machine) and any other faucets that he can (again, just shut shut off under sinks). After everything is isolated test the water heater at a single faucet and then open one valve at a time until you find the faucet/valve causing the issue.

Single lever tub/shower valves (mixing valves) can not usually be isolated and may actually be the culprit here so be sure the plumber keeps that in mind. In other words, if he isolates everything and is sure there are no other cross connections and you still have the issue then one of the tub/shower valves is the culprit and the mixing cartridge is the issue... ;)

I'm pretty sure this is the issue... just need to find the right faucet/valve or outside faucet (if fed hot and cold water, right?) causing the issue!

Back to you...

Mark