Why is my gas hot water heater not working?

A pilot light going out is a common problem if a gas water heater isn't heating. It could be caused by the gas valve, the gas supply, or the thermocouple located next to the pilot light.If a gas water heater does not heat up, the common problem is that the pilot's light has turned off, which may be due to the gas valve, the gas supply, or more likely the thermocouple next to the pilot's light.