My Insinkerator instant hot water heater sputters when the water is turned on
I tried flushing the lines as directed in the manual, but it still sputters with air in the line whenever it is turned on.
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I found the cause of the sputtering problem for my insinkerator hot water dispenser! If you take the unit apart (there are instructions and videos online, but it's not hard), you find a small plastic tank at the top of the hot water tank. The tub connected to this is where air enters the system, via the small air hole under the the faucet (at least on my setup). This plastic tank has a one way valve at the bottom. I could see that this whole valve area had lots of black stuff (probably black algae) and guessed that it was blocking air from entering the system. If air can't get in, then it will enter from the main faucet nozzle, which will cause sputtering. I cleaned out the black algae as well as hard water deposits by running vinegar through the plastic tank using a small fountain pump, in a closed loop. Left it that way for an hour or so, then banged it around until I could get all of the algae and deposits out. I then put it back together and it doesn't sputter now! (Well, maybe it'll sputter some if you use a lot of hot water very quickly, so maybe the valve isn't completely clear, but it's definitely much better and doesn't sputter most of the time!)
(So, the TLDR is: the plastic tank inside can get clogged with algae and/or water deposits. Clean those out with vinegar and it goes back to working!)
This worked for me as well. There was one tiny screw at the top and that was all that was required to open up the case. The plastic tank on the top is removable; there is where the problem lies.
The funnel-looking outlet is normally pointed down, and was filled up with black stuff.
Check to see if the water temperature is set too high. Does the water feel too hot when it comes out?