Burner in Aliance 501 water heater keeps turning off after it heats up have to light pilot back on

See if big red knob has a PILOT or LIGHT setting and put it on that setting. Next look at knob on bottom-- it should have a circle cutout on it that needs to align with the pilot push button. The cutout lets the button be pushed in. While holding button in---light the pilot and keep holding the button in for about 3 minutes. If everything is working right with the water heater, after 3 minutes or so you can let go of the button and the pilot should remain on. If it stays on. turn the smaller button to the run or heat position and the big burner should come on. Then set the big heat control knob for the heat setting you want.

If your pilot is lit, and you have valve turned from pilot to ON, and thermostat is up on warm or hot, and you still don't have main burner on, then you have bad gas valve (the square thing with temperature and on/off/pilot). These unscrew from water heater and can be replaced, but keep in mind that they go directly into tank, so shut off water and drain unit first!

Btw, I’m available to help over the phone in case u need at https://www.6ya.com/expert/perry_14036f9bc71cde6a

Reliance
2nd and 3rd digit of serial number is year
C05 is 2005

What color is flame? Should be clear blue.
Pilot is burning so thermocouple is good, and sitting in pilot flame.
Pilot flame should be clear blue.
Otherwise clean burner parts.

Is water at tank hot??
If burner is not turning on, the gas control thermostat is probably bad.
http://waterheatertimer.org/pdf/How-to-replace-water-heater-gas-valve.pdf

Otherwise more information is needed.
http://waterheatertimer.org/How-to-troubleshoot-gas-water-heater.html

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

Reliance water heater?
Thermocouple is good if the pilot stays lit continuously.

501 is older model. Unknown if this unit has FVIR protection and sealed combustion chamber or open air intake on front of unit.
http://waterheatertimer.org/pdf/Reliance-2006-Service-Handbook.pdf

With FVIR protection:
Get more fresh air to the unit.
Clean the flame arrestor screen.
Test and replace the thermocouple:
http://waterheatertimer.org/How-to-test-water-heater-thermocouple.html
Inspect and clean burner and combustion parts
Test gas pressure, bleed air out of gas line.
Replace gas control valve.
Test draft air by lighting match and see if smoke is pulled into the vent pipe at draft hood on top of tank.

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

You need a new gas control valve.

Hi,

To change a gas hot water heater thermostat you will need to first buy a new gas valve for your hot water heater. The gas vaive and the thermostat are integrated into one unit.

To replace the thermostat on a gas hot water heater you must follow these procedures....

1. Turn off the incoming water and drain the water heater.

2. remove the pilot tube, the burner gas tube and the thermocouple from the gas valve. Turn off the gas line and remove from the gas valve.

3. get a pump pliers or a wrench in behind the gas valve and turn the whole assembly CCW to remove it from the tank.

4. After appliying pipe dope or tape to the new gas valve threads, turn the new gas valve into the tank by turning in a CW direction. Be careful not to damage the small wires to the ECO. They are the little red wires on the back. If you break them the assembly is irreparably damaged.

5. reinstall the gas line, thermocouple, burner tube, and the pilot tube to the gas valve.

6. Fill tank with water. Make sure to open a hot water faucet and purge all air from the tank.

7. Check for leaks where the gas line hooks up with soapy water.

8. Relight pilot light and check operation.

9. Set the new temperature setting to a medium setting and then adjust the temperature to your likeing from there and adequate time for heating completely.

heatman101

The paid answerers might have a specialist in your model of water heater.
As a free answerer, I specialize in providing resources that might help you for free.
When you say the gas control pieces, I assume you mean you replaced your entire gas valve with a generic dial-type gas valve.
You replaced thermocouple, but you did not replace burner assembly that includes the pilot tube.
Your other gas appliances are working fine.
You have not installed a new gas furnace with a blower that is vented up the same chimney as the water heater.
You have put your hand near the vent hood to see if there is backflow coming into the water heater when the furnace turns on.
You have removed the vent hood to give you access to the vent pipe, and you lit a match and the smoke from that match drafted upwards. You have done the lighted-match test when the furnace turns on which reveals the general condition of the venting stack.
You have checked your outdoor vent stack to make sure there is no obstruction, or the vent hood is not missing.
The burner flame on the water heater is a clear blue color with very little yellow. This shows the quality of the combustion air and reveals if amount of gas flowing to burner is restricted.

http://www.thetankatwaterheaterrescue.com/forums/forum3/

http://www.reliancewaterheaters.com/prod/gas.html
Reliance is an AO Smith company
The site doesn't have a manual for the 501
I e-mailed Reliance several weeks ago asking for a 501 manual.
They send a generic gas water heater manual with no troubleshooting

http://www.reliancewaterheaters.com/lit/om/g616.html
Link above shows a typical Reliant heater, the 616
Age of your water heater can be seen on serial number.
The two numbers following first letter are the year water heater was made.

http://www.reliancewaterheaters.com/lit/om/manuals/186486-002.pdf
Troubleshooting begins on pg 29
Troubleshoot flowchart begins on page 31
The new gas water heaters have the FVIR system so troubleshooting includes that information.
I don't think the 501 would have a FVIR flammable vapor prevention because it is older
The new systems have an igniter
The troubleshoot flowchart gives valuable information

turn the dial to pilot and push and hold down red button while you light the pilot located inside water heater beside burner, keep holding button down after pilot is lit for about 1 minute. If you let go and pilot goes out repeat above steps and make sure pilot flame is heating up the thermal couple. If that fails replace themal couple.

Hi I would try changing the thermocouple

The pilot assembly should look similar to the pic above. Depending on where you live, you may be required to hire a certified plumber to replace the parts. If not you can do it your self. Keep in mind if it's not staying lit you also need to check the thermostat and the thermocoupler before replacing the pilot assembly. There is a good chance it is just the thermocoupler going out. It is one of the first things to check when troubleshooting a pilot light problem with a gas water heater. A thermocouple determines if the pilot light is lit. If it's not lit, the gas valve fails. If that's the problem, replace the thermocouple.

1. Shut off the gas valve on the water heater and the gas valve on the line near the heater. Remove outer and inner doors, and loosen the pilot and supply tubes and the thermocouple connections to remove the burner assembly.
2. Step 2 Loosen the screw holding the thermocouple to the bracket. Remove old thermocouple. Bring it with you to the store to ensure you are buying the proper replacement.
   
3. Step 3 Install the new thermocouple. Position the thermocouple so that the pilot flame heats 1/2 inch of the tip.
   
4. Step 4 Reinstall burner assembly in the water heater. Tighten burner supply tube, pilot tube and thermocouple connections. Tighten thermocouple no more than a quarter turn more than hand-tight.
   
5. Step 5 Turn on both gas valves. Check supply tube and pilot tube for leaks with soapy water. If soap bubbles, tighten connections to fix leak. Ignite the pilot light, and make sure the thermocouple tip is heating up. Replace inner and outer doors.