I have a single handle Delta shower faucet (shower only, no tub) that gets hot water for less than a minute and then goes all cold. Someone told me there is a regulator that can be adjusted. I have no idea where it is and how to adjust it.

Is this problem only on the shower? Or does it happen to other fixtures? How old is your water heater? Is it electric or gas?

All the other fixtures are fine, my water heater is gas and fairly new, it is set now to 170 degrees.

I would be severely skeered of 170 degrees in my home. You can become a crispy critter rite quick that way. You also are going to be replacing your t & p soon. And your plumbing ain't going to like it. Many bad dreams in your future.
The first thing I would try is to take the handle off and see if there is a handle limit device. This stops the handle from turning all the way to full hot. This device is a small plastic piece just setting on the stem assembly. It is used as a scald guard to protect children and older people. I strongly suggest readjusting it but not removing it.

I took off the handle and adjusted the limit device. FINALLY HOT WATER!! Great simple advice. Thank you. T&P?

Doug... sun one ask you what a T&P valve is in the post above, I am not sure you saw it. .

Tom and the others have given much advice about t & p valves. It is the brass thingy that has the third pipe connecting to the water heater. It is heat [temperature] and pressure [pressure] sensitive. By having the temp at 170 you have softened the spring and if so it is much more sensitive and prone to failure.

O.K. Now that we have figured out the first problem, where is this little spring and how do I change it? You guys have been excellent help so far.

Keep going Doug... you are doing good... hahahaha

170 Degrees?

Yikes!!

The T&P valve has no user servicable parts, so replace it and lower the temperature to 120 degrees before you come home to a swimming pool.

Sun, on your water heater are 4 connections. You have a cold inlet and an hot inlet typically on top. 3/4" pipe is connected to this. you also have a power source. one has gas with a gas connection about knee high on front. one has an electric connection typically on top. and very few have a forced vent with a fan which uses 110 volt that powers the fan mounted inside the vent on a gas water heater. these are the typical things you will find. there are more but those are not typical. the last connection is the temperature and pressure relief valve also known as the T & P. this is sometimes located at the top of the heater and sometimes located at the side. regardless, it is made of brass and it also has a 3/4" pipe connected to it to carry hot water to be disposed of to a relatively safe place in case of it releasing water. This protecting device may have become compromised by the excessive temperature and it may not be defective but I suggest you simply call around to a few plumbing companies and simply ask them to quote you a price on the phone on how much it costs to change it out. At home depot this device is about 7 or 8 dollars. I sell it for 12.96. The parts needed if you cut the pipe loose should be less than 5 dollars. But, for the sake of argument, let's say the parts will cost 25 dollars. The whole job of turning the water off and bleeding it down and replacing the part and reconnecting the connecting pipe and turning the water back on and flushing out the system should take an hour. Get a phone quote from at least 5 licensed plumbers and simply have it done. This is simply an ounce of prevention.
On another note, I like helping people understand the problem they are facing but if you are not qualified to do plumbing, in some cases you are putting much at risk. If you do your own plumbing then you risk the work not being covered by your homeowners insurance and if you are working with gas or electricity you are risking your life and the lives of others. The reason skilled trades are expensive is because we have paid the price for our experience and the cost of doing business is expensive. A plumber that gives you a very low price is likely to not be licensed and probably not insured or paying taxes. You have the right to request proof of license and proof of insurance. You are remiss if you do not.