Water heater pilot lights but burner doesn't ignite

with any hot water heater I have seen, there is a on/pilot/off valve. you rotate the selector to pilot, depress the plunger and press the igniter. but then you have to hold the pilot button (not the ignitor button) and let it run for a few seconds to warm up a little sensor inside that says the pilot is indeed running. then, once the sensor has let the pilot run constantly (instead of winking out), you rotate the valve to the on position and everything should run fine. otherwise, there's a different protocol for your unit or it might need servicing.

If I understand correctly, your pilot flame is lighting correctly. But the main burner won't turn on because the electronics in the Gas Control Valve don't acknowledge the pilot is lit.

There are two likely faults:

1. Thermopile is not sensing the flame correctly, or
2. Circuit Board in the Gas Control Valve is defective.

To test for case 1, use a multimeter to measure the Thermopile output. It should be at least 350mV. Here are instructions on how to do that:

http://waterheatertimer.org/pdf/Test-thermocouple-and-thermopile.pdf

If the Thermopile output is less than 350mV, you may remove it from the burner and clean off any corrosion.

If the Thermopile output is adequate, the fault lies within the Gas Control Valve. Unfortunately, there are no user-serviceable parts in there, so you would need to replace that entire assembly.

Don't replace a thing until you remove main burner. Use compressed air to blow out burner gas line and jet. That was my problem. The burner would not light so I blew the line out and now it works fine.