My gas water heater has been hissing non-stop for several days now, and it seems to be getting louder. I have flushed the water heater but the noise remains. From diagnosis, the hissing seems to be coming from the bottom of the heater. The meter outside tells me there is no water leak and the heater itself is not leaking. The age of the heater is probably 6 years or less.

Any ideas?

Shut off the gas valve, if the sound stops the second the flame goes out I'd suspect a dirty gas oriface. The gas escaping to the flame can create a sound if its partially clogged. Clean I or replace it. The arrester is not that difficult to clean. How I Cleaned a Richmond Water Heater Flame Arrestor Screen - YouTube

I turned the red knob to the "off" position, the pilot light went out but the hissing remained. I called Rheem and found out my warranty expired 3 months ago. Other than generic advice they were unable to help me. I fear the time may have come to purchase a new heater.

BTW, my heater is in my utility room on the floor. My utility room is tiled with peel and stick tile. Should the heater be elevated or is it okay on the floor?

Heater comes with legs that raise it to a sufficient height for tile floors. Leave the gas valve closed for now and periodically check for the sound, let us know how long it takes to dissipate

It's been 30 minutes or more since I turned the knob to the "off" position, and the hissing is still as loud as ever.

OK that was 2 hours ago. If it is still hissing shut off the fed line to the heater and open a hot tap somewhere. Does this stop the hissing?

I did that, it's still hissing. The only thing left I can think to do is to tear down the water heater so I can look at the bottom. The sound is definitely coming from there, so maybe it is some type of clog underneath.

Thank you very much for your time in this matter. I'll let you know the results.

Thanks again!

If the gas is off, the water supply closed and a tap is open then I would say the sound is not coming from the heater. Could be a echo bouncing off the heater or down the exhaust tube. Since it is a gas heater you can open the door to the flame area and remove any other doors installed to protect the flame. Flashlight and a small mirror will help but I am starting to think the heater is not the issue. Good luck

My gas water heater is leaking from the bottom its making hissing noises, and the pilot light went out

Cd, if you described this correctly there is no fix. Replace the water heater.

No fix like Bob says, please tell us the brand and the model number of you heater, and how old is you heater? Thanks.

John