Likely cause: the pilot light is out: water heater no hot water

Why this happens

Bob Vila lists an unlit pilot as a common reason a gas water heater gives no hot water, and says that if the pilot will not stay lit the thermocouple may be at fault, which is a job for a pro. A. O. Smith lists thermopile issues, dirty inlet air screens and fuel supply problems among the causes of no hot water on gas models. Because relighting involves the gas burner compartment, this site treats it the same way it treats a furnace pilot: a licensed plumber or your gas utility relights it, not you.

What to do right now

Make sure there is no gas smell. If there is any, leave the house now and call the gas utility or 911 from outside; do not flip switches or use a phone inside.
Look for the status light or a small window on the gas control. No flame and no status light means the pilot is out; a blinking status light is a code the technician will want.
Check that other gas appliances in the house still work. If none do, call the gas utility first; the supply may be off.
Do not try to relight it yourself. Turn the gas control knob to off, following the label, and call a licensed plumber or your gas utility to relight it and check the thermocouple.
Give the tank an hour or more to reheat after the pilot is relit before you judge whether the heater is fixed.

When to stop. Any gas smell at any point means leave and call from outside.

What to tell the plumber

It is a gas water heater with no flame, and whether the pilot relit and stayed lit.
The make, model and age from the data plate.
Whether other gas appliances in the house are working.

Build the full list: what to tell the plumber.

Start this troubleshooter over

References (every fact above comes from one of these pages)

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