Our Kenmore 2013 gas water heater was making a hissing sound. I found out when I turned off the water to the water heater, it stopped and the water meter stopped turning. We did not use any hot water so it was not just refilling due to usage. It also runs constantly.. We also found the water was not as hot.
I read other posts that there may be a leak under the slab, which we are on. I don't think this is the case since no pipes go under the slab except the separate hot baseboard system, which is separate.
The hot water heater has a warranty but if the problem is something else, I would have to pay. If a pipe was leaking, I would think I would see it leaking somewhere. Tomorrow I am going into the attic where I possibly can see some of the pipes. Any suggestions?

 

A water heater cannot use any water. Water goes in.... gets heated... and comes out.

If you turned off the cold water supply to the water heater and the hissing noise stopped......
you have a leak in the hot water pipe. If you don't see water..... good chance it's under the slab.

Doubtful there is plumbing in the attic.
If there was and it was leaking.... you'd know on every floor below it.

 

It could be leaking into the burner compartment, and getting evaporated by the burner.
As said above, your water heater doesn’t refill. Water instantly replaces what’s being used.

 

Thanks for the replies. If I turn the water heater off but leave the water on, will that be enough pressure for it to leak under the slab? Maybe this can tell me if it is leaking inside the heater or under the slab. Since cold water seems to go into the heater, we don't have that real hot water. Can I turn the water off for a time if I don't use hot water or if it is on, can that ruin the water heater if it does empty? Sunday is not a great day for plumbers. I will check around the house to see if I see any wet spots. Seems like this can be a really big issue. I wonder if it is covered by my homeowners. .

 

You cannot leave the burner on if the water is turned off.

 

Unless a catastrophic disaster such as the HW tank exploding, homer owner's insurance will not cover it. A HW tank that's leaking or mal functioning, especially after several years is considered normal wear and tear.
I like Roughtneck's explanation that the hissing could be a very slow leak internally hitting the burner section. Also the lack of hot water could be a sign of a deteriorating dip tube or anode rod (depending on gas or electric). Your tank is at 8 years which falls into the average of 7 to 10 years life span of appliances. If you have a 12 year warranty (most are 6 year) then you may get manufacture warranty if you can prove poor manufacturing or workmanship. But the manufacture might contest the warranty if you can't prove regular maintenance, normal water conditions (not extremely hard water), proper plumbing practices and installation.

 

Get a good strong flow of water out of a hot faucet upstairs before turning the water heater heat back on.

With the burner shut off, water leaking into the combustion chamber will not evaporate quickly and will leak out onto the floor soon.

A leak in the hot water plumbing is a very common cause for excessively high water and gas (or electric) bills.

 

If it is enough of a leak to be seen on the water meter..... extremely doubtful the tank is leaking on the burner. A tank leak typically makes it self known very quickly.

Here's a test..... don't use hot water for several hours or do this in the morning.... check the hot water line leaving the tank. The line that has the leak will be hot.

 

You may want to make sure no water is being used and then go to the meter. Check for flow. If glow is seen go to the water heater and close the incoming cold water valve. Now go back to the water meter and check for flow. If none indicated it sounds like you have a hot water line leak. Especially since you said the burner is on constantly and water is not hot.
Wishing you the best

 

I turned it on vacation mode. Then noticed the leak coming up from the slab between the walls. Cancelled plumber from warranty company and calling someone else. Thanks for the advanced warning of a slab leak. Homeowners insurance will cover part of it. I guess they have to jack hammer the floor.

 

Sometimes they jack hammer the floor.
Sometimes they try running PEX (flexible tubing) a different route.