How does a natural gas water heater works?

i have a SURN water heater and trying to repair it. i changed the small leaking gas tube and installed a new thermocouple but the main gas tube doesn't work. what is my problem?How does a natural gas water heater works?
First----Do you mean a Zurn water heater instead of Surn?

Two----Is it a 2003 year model or newer?

Three---What was the initial problem for you to begin repairing?



Let me know. I'll reply tomorrow.How does a natural gas water heater works?
when you light the pilot light, and when you release the button , does the pilot light stay lit ? then turn the gas knob to on, check temp setting, is main gas valve on/
Check http://appliancequickfix.com/
When you turn on your heater do you see a bright glow? If not than replaced your ignitor and this will correct your problem.
Don't mess around with this one, If you play with fire, you may get burnt. Call a Pro or get a new heater. You could Die from a gas leak, or blow up your house.