What does sediment mean

After extensive searching there is no procedure shown. Presumably, you leave it, or you remove it from the installation, turn it upside down and shake it. Then put CLR and water in it to descale it, then rinse and reinstall. Hot water storage tanks have a drain at the bottom and an access hole from the element. After a year of use there should be nothing in it.

You could phone the maker / distributor and ask?

https://www.google.com/search?q=Little+Gourmet+Instant+hot+water+dispenser+clean+out+the+sediment

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I'm not sure what you mean by "gurgles when refilling." If you mean that it is making noise when heating the water, that is usually a sign that sediment has built up in the bottom of the tank. This results in the surface of the tank bottom to overheat and the sound you hear is the water flashing to steam. This usually results in tank failure as the glass lining will crack an the tank will rust out. If it's not too late you could drain and flush the tank to try to remove the sediment but if has hardened to a solid mass it won't come out.

If you clean sediment out of tank, it will restore full efficiency to electric water heater:http://waterheatertimer.org/Clean-sediment-out-of-water-heater.html#electric
http://waterheatertimer.org/How-to-clean-sediment-out-of-electric-water-heater.html
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Rumbling sound usually means sediment build-up inside tank.
Yeas a leaking water heater is dangerous because it can cause water damage.
Copy following link to determine source of leak.
http://waterheatertimer.org/Leaking-water-heater.html
http://waterheatertimer.org/Clean-sediment-out-of-water-heater.html

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

The way it is designed on the water inlet it is supposed to cause the water to swirl around the tank wall to help keep sediment from building up. I would still recommend draining and flushing every couple of years if your water has a very high mineral content. Thank you.

You posted under electric water heater.

1) Gas or electric, the noise is from sediment build-up inside tank.
Once sediment builds up, the only way to solve problem is to clean the tank out.

2) To restore full efficiency to electric water heater and stop the noise, clean the tank:
http://waterheatertimer.org/How-to-clean-sediment-out-of-electric-water-heater.html
3) To clean gas water heater is more difficult and less successful:
http://waterheatertimer.org/Clean-sediment-out-of-water-heater.html

4) To prevent sediment problem, flush water heater each 6 months before sediment can build up.
http://waterheatertimer.org/Clean-sediment-out-of-water-heater.html#flushelectric

5) Other things to know for water heater maintenance.
http://waterheatertimer.org/Replace-anode-rod.html
http://waterheatertimer.org/9-ways-to-save-with-water-heater.html

The crackling noise is from build-up of sediment.
I forget exact reaction that causes the noise.
Water heaters exposed to hard water will create sediment inside the tank.

Following link shows sediment and remedies for gas and electric water heaters.
http://waterheatertimer.org/Clean-sediment-out-of-water-heater.html

Add a comment for more free help.
Also take advantage of fixya phone service.
For a price, expert speaks with you over phone while you work on water heater or any do-it-yourself project.
Fixya is always less expensive than a service call.

There are two water lines connected to water heater.
One is marked Hot and the other Cold.
The shut off valve is on the Cold line.

To eliminate sand and dirt from entering your water heater, the 'sediment' filter should be installed on Cold line.
Sand and dirt are sometimes called sediment, but this type of sediment is not the same as calcium carbonate sediment that accumulates inside a tank that receives hard water.

When you have hard water, then water heater makes calcium carbonate 'sediment' deposits that accumulate in bottom of tank. A 'sediment' filter will not prevent this problem.
http://waterheatertimer.org/Clean-sediment-out-of-water-heater.html
http://waterheatertimer.org/How-to-clean-sediment-out-of-electric-water-heater.html

If you have hard water, to prevent calcium carbonate from forming inside tank, you need a water softener.
Water softener will prevent calcium carbonate sediment forming inside tank.
However water softener will shorten life of water heater anode rod.
http://waterheatertimer.org/Replace-anode-rod.html

Add a comment for more free help.
Also take advantage of fixya phone service.
For a price, fixya expert speaks with you over phone while you work on water heater.

Is this gas or electric heater?

Gas heater, the thermostat might be bad.
You might need to change out gas valve.
Also look in and see if flame is light blue or yellow.
Blue is good.
Yellow flame means you need to clean burner, or replace burner.
Burner should be cleaned each year.
Refer to manual for instructions and parts list.
http://www.whirlpoolwaterheaters.com/support/Manuals.aspx
Also tank might be filled with sediment.
http://waterheatertimer.org/Clean-sediment-out-of-water-heater.html

Electric water heater is different altogether:
Some hot water means upper element is working.
Water heater ECO reset button is good.
Tank is not overheating.
Electricity and circuit breaker are good.
Remaining suspects:
Thermostats are bad, loose wire, shorted wire, lower element burned out, sediment inside tank.

I test instead of guess:
Here is 30 minute troubleshoot overview that will identify problem and show how to repair electric water heater.
http://waterheatertimer.org/How-to-troubleshoot-electric-problems-with-water-heater.html

With Rheem you have to back to the installer.Most of the heater have ten year warrany.