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Is the exhaust fan running? can you give me a picture of the gas valve and related controls? Click on ADD FILES next to the SEND button to post a picture here
The draft fan should start automatically as soon as there is a call for hot water. If the fan doesn't run nothing else will happen. You need to check all the electrical connections. If they are all good then fixing this is probably not worth the expense given the age of the heater. You could have a bad exhaust fan or gas control valve. Both components cost several hundred dollars and are obsolete and may not even be available not to mention that the tank could leak at any time given that it's 12 years old.
The average expected life of a gas fired water heater is 8 to 10 years
If you tell me the LED flash sequence (how many times does it blink before it pauses and repeats) I can tell you what error it is displaying. We can also do some trouble shooting if you like. You'll need a multi-meter to do this.
Also try turning the ON/OFF switch on (if it's not on already) and off a couple times