I've tried to light my hot water heater but it goes out when I release the red button can you tell me if I need to replace the core ?

I've tried to light my hot water heater but it goes out when i release the red button can you tell me if i need to replace the core ?
My hot water heater want light

You need to replace the thermocouple. If that doesn't do it, then the gas valve is defective...

Before you replace the gas valve, make sure the pilot flame hits the thermocouple. Also are you holding the button down for a minute after lighting the pilot?