hot water tank

i have been running out of hot water when i take my shower...normal shower...nothing kinky. the plumber i have been working with suggested replacing the dip stick to start, which he did. same problem. replaced the tank. problem persists. he came out to troubleshoot and determined that i am only getting 6 minutes of hot water out of a 40 gal tank. did some testing and thought that i was not getting enough gas pressure. per gas co pressure is fine. still running out of hot water. help?

It could be any number of things... However, It sounds like your plumber is not doing a very good job of diagnosing the problem. Some other causes that come to mind are an under the slab hot water leak, or, a hot/cold cross connection. Are you on a slab foundation?

Lets do a basic test. Run the shower until it runs out. Leave it running and check the lav faucet hot to see if it has also gone cold. Then check the pipe on the outlet side of the water heater and see if that is cold. Post back with your answers.

Take a bucket and a watch and measure how much water goes into the bucket from the showerhead in a minute. If the bucket is too small, try going for 30-seconds, then multiply by 2. WIth a 40-gallon tank, you should be able to get about 28-gallons of hot before it starts to significantly cool off. Depending on the thermostat setting, you may be mixing a bunch of cold with the output, so you should be able to actually use more than that at the showerhead (since it would have some cold mixed in). Current showerheads are limited to 2.5gpm, but an old one, or a multiple head system can use significantly more.