Water Heaters - HELP!!! 2nd new water heater and still not enough hot water!

HELP me please. I had a Home Depot contractor replace my 12 year old water heater because I was not getting enough hot water, approx 5 minutes of shower use then cold. After the contractor replaced the old unit with the "Best" one Home Depot carries the problem did not go away. I had good hot water for the 1st day or so then by day 2, 5 minutes of hot water then cold and it takes FOREVER to recover. The technician then came back out, installed another new unit and again we are back to the same issue. I called an electrician and they checked all the connections and the voltage, amps, and ohms at the water heater and they all checked out. What could be the problem? I am at a loss. Please help, I am about to loose my mind. :wall:

This is a long shot in the dark, but you don't by any chance have a one-knob shower control do you?

Second long-shot idea [and I can't imagine they would have screwed this up] are the inlet and outlet of the water heaters connected to the proper plumbing and not reversed?

Thanks for the quick reply:

Both of our showers are one knob controls. Does that matter? Plus, if we wash dishes in the kitchen sink, the same symptoms occur. We did not have a problem until about 2 weeks ago when the old water heater obviously died slowly. In regards to the inlet/outlet reversal, I am not sure. The Regional Manager of the contracting company is coming out to inspect but I want to make sure that all my stuff is OK before I start shooting! Please help! :madhell:

You might try turning the shower to full hot and letting it run. If it goes cold after 5 minutes, check the temperature of the outlet pipe at the water heater. If it is cold then the water heater isn't doing much (even with a tankful of cold water, if the elements are on you should at least be getting warm water). If this is what happens, then there is strong evidence that the water heater is not operating properly (defective, or incorrectly installed).

If the outlet pipe is hot while you are getting cold water from the shower, then there is a strange plumbing problem. This would mean that the water heater is heating the water but it isn't getting to the shower. The earlier question about the "one knob" shower control is because it could be malfunctioning - more likely if it is a constant temperature type. Beyond this, it gets really peculiar (You don't have a circulation pump do you? This would be quite unusual on a residence.)

Be sure to post back here when you find out what is haywire.

So the saga continues....After the water heater contractor came out for the 3rd time, they suspected a leak in my hot water pipe. So I pulled open the crawl space and to my dismay I hear the hissing of water. So after the pipe was repaired by a licensed plumber the hot water returned....so I thought. I work nights so after being up ALL DAY getting this problem resolved I finally get to sleep for 2 whole hours. So when I wake up to go to work my wife informs me that there is no hot water. :wall: I go out to the water heater and the ECO is tripped and the unit is not working :madhell: ! So I press the reset button and it seems to be working now but I told my family not to use any hot water until tomorrow to let the tank refill. So the saga continues....:wall: