My heaters pilot wont stay on and ive replaced the thermocoupler and pilot assembly and replaced the gas valve and it still wont stay lit what could cause that? and its a teledyne laars lite llg series

Have you tried cleaning the inside of the valve where the thermocouple enters? Often there will be corrosion there and it will not pass the tiny amount of voltage required to activate the safety feature.

If it's not the thermocouple, then the control valve might have failed. There isn't much else that can cause this.

This could be due to a bad thermocouple, dirty pilot assemby or a bad gas valve. Clean the pilot assembly and replace thermocouple first since it is inexpensive, and they should be replaced every few years. If this does not help a new gas valve will be needed.

Thermocouple has failed., replace thermocouple or dirty pilot assembly, not enough heat being genrated to produce the 30 mili volts D.C. current to hold the pilot valve open. Clean pilot orfice. Remove assembly and pilot tubing from gas valve. Blow into pilot tubing to remove dirt.. Make sure pilot flame is engulfing the thermocouple.

take out the pilot assembly. there is a small burner and an orfice. the orfice does get clogged if it has not been operated for awhile. you can clean it out with a small sewing needle. if the pilot wont light or stay lit, replace the thermocouple.

It sounds like your flame detector (usually a thermocouple) has gotten weak and when you cleaned the pilot the stronger flame was able to generate enough power to keep the gas valve working. If you replace the thermocouple your problem should go away. If a new thermocouple will not keep the gas valve operating...the coil in the gas valve has gone bad and you will need to replace the gas valve assembly. (most valves do not have replaceable coils).

Sounds like the thermocouple is bad , if , your holding the ignitor pressed long enough . Rating of 1 - 10 , this would be a 4-5 . Don't replace the pilot assembly , just 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.
   

If the pilot flame does not touch the thermocouple, the heater will do exactly what you describe.

Get a short piece of copper tubing that will fit snugly over the thermocouple and bend the short piece so that it is in the pilot flame.

Clean the pliot light tube with a Q-Tip and alcohol. Clean 2 inches deep. This will increase the pilot light flame and it will heat up the thermocoupler so it will stay lit.