InSinkErator SST Instant Hot Water Dispenser

DIY: Instant Hot Water Heater with Low Flow? Fix it with a Flush! 61

Flush your Instant Hot Water TankAn undersink instant hot water dispenser (like my InSinkErator SST) is one of those kitchen luxuries you may not think you need until you get one… after which, you’ll never know what you did without it. But after a few years, I noticed that it was taking longer and longer to fill mugs, pots, or ramen bowls with near-boiling hot water from my InSinkErator faucet, as the once-steady flow was now reduced to a sad trickle. 🙁 After thinking back to my DIY hot water heater flush project with my whole-house hot water tanks, I figured I’d try a similar approach to fix the low flow on my InSinkErator SST tank.

InSinkErator SST Instant Hot Water Dispenser

InSinkErator SST Instant Hot Water Dispenser

Of course, depending on the brand and vintage of your instant hot water dispenser, your model’s connections and details may vary, but the principles will be the same. Basically, you need to disconnect your tank, drain it, flush it, reconnect it, refill it… and party with hot water. The entire process (except for letting the hot water cool before you start) should take less than 30 minutes.

Unplug and Wait

First, I unplugged the electrical cord from my instant hot tank and waited. In fact, I unplugged it at night right before going to bed, and then did the rest of this procedure the following morning. The important part is that you unplug the unit and allow the water in the tank to cool before doing anything else. Boiling hot water and DIY projects don’t mix.

Clean and Prep

With all under-sink plumbing projects, I removed everything from under the sink (which is always a good excuse to purge stuff you’ve stashed under there and no longer need) and placed a towel under the area where I was working. If you want to keep your wife happy, I recommend not using your “good” bathroom towels from the guest room. I used one of our beach towels instead.

Disconnect and Remove the Tank

After allowing the hot water to cool completely, I found the shut-off valve that connected cold water to the tank and turned it all the way closed. Although, in my case, the shutoff valve doesn’t actually connect directly to the tank. Instead, it connects to the InSinkErator faucet above, which feeds cold water to the tank only when the InSinkErator faucet is turned on. Therefore, technically, I could have got away with this procedure without shutting off the valve at all.

Next, I looked at the three connections on the top of my InSinkErator SST tank. Here’s what they look like:

InSinkErator SST Connections

From left to right: cold water inlet, hot water outlet, air vent connector.

The blue tube on the left connects to the tank’s cold water inlet, the silicone tube in the middle connects to the hot water outlet, and the clear plastic tube on the right connects to the air vent. Removing all three tubes required no tools: a thumb press released the quick-connector on the cold water tube, and some gentle tugging and twisting removed the other two.

My tank was mounted to the side of my under-sink cabinet by two screws. I loosened them, but didn’t need to remove them all the way, since the plastic mounting bracket had large holes (see picture above) that allowed me to lift the tank and guide it off the screws. Tank removed!

Check the Inlet First

Shining a flashlight down into the cold water inlet on my tank, I could see that the opening was almost completely blocked by hard water deposits. Using a small jeweler’s screwdriver, I pressed down gently and unblocked a tiny hole in the middle of the inlet, which is probably only a millimeter or two in width. I was surprised that only a small part of the inlet was actually open to allow water into the tank, but I’m thinking that maybe it’s designed this way to act as some sort of flow restrictor, which allows the cold water to come into the tank in a tight jet and send cold water to the bottom of the tank more efficiently — and maybe helps with faucet pressure.

Drain and Flush

After unclogging the inlet, I held the tank over my sink and flipped it upside-down to allow it to drain. That’s when I saw the stainless steel drain screw on the bottom of the unit. 🙂 Always be careful any time you’re removing screws over any type of drain. Drains are like black holes to screws: they suck them in, and you’ll never get them out!

I unscrewed the drain screw (being careful not to lose the rubber washer or drop the screw down the drain), and flipped the tank upright to let it finish draining. I had to shake the tank a couple of times when the flow slowed down, meaning there was probably lots of hard water deposits and sediment inside that were contributing to the tank’s reduced flow. After the first draining, here’s what was left on the bottom of my sink:

Small Particles from the First Draining of the Tank

Small Particles from the First Draining of the Tank

You can see a few larger chunks of calcium, but the majority of what came out was fine sand-like particles. I re-installed the drain screw, hung the tank back on its mounting screws under the sink, reconnected all three tubes, and turned the shut off valve back on. I didn’t, however, plug in the electrical cord. No need to do that until the very end.

I opened the faucet and could hear cold water flowing into the tank, as well as air flowing out of the faucet as the tank filled. Rather than holding the faucet open, I used a screwdriver handle to force the faucet open until water started to flow, like this:

Lazy Man's Method of Holding Open the Faucet

Lazy Man’s Method of Holding Open the Faucet

Already, I could see a massive improvement in the water flow from the faucet. I let the water run for a minute or two, then removed the screwdriver to shut off the faucet. I disconnected everything again (without closing the cold water shut off valve under the sink this time), brought the tank back up to the sink, removed the drain screw, and drained it a second time.

During the second draining, I shook the tank occasionally to try and agitate some of the hard water deposits inside, and kept flipping the tank over to let it alternate between draining from the top and the bottom. The first draining had removed most of the sand-like particles, so I got lots of bigger chunks out of the tank the second time:

Hard Water Deposits from the Second Tank Draining

Hard Water Deposits from the Second Tank Draining

I repeated the fill and drain process one more time, and got clear water out on the final drain.

You might be tempted to pour some mineral remover (such as CLR or LimeAway) into the tank to help dissolve the deposits, but I don’t recommend it. That stuff is crazy toxic, and even if you let the unit flush for 15 minutes or more after reconnecting everything, you just can’t be sure that you got it all out. Plus, it tastes super nasty. How do I know? Don’t ask…

Final Re-Assembly and Test

After the final draining, I reconnected everything one last time and used my screwdriver trick to refill the tank and let flush out for about 10 minutes. During that time, I removed the nozzle on the end of the faucet and used my jeweler’s screwdriver to help remove hard water deposits that had collected in the screen.

After a good final flush, I turned off the faucet, screwed the nozzle back on, then plugged in the electrical cord to let the tank start heating again. Fifteen minutes later (which was slightly longer than it took me to put all the cleaning supplies, dishwasher detergent, and spare garbage bags back under the sink), I had piping hot water flowing briskly from my InSinkErator instant hot water dispenser!

This DIY project only cost me 30 minutes of time and no money in parts. That’s way better than $188 for a replacement tank from Amazon, or a spendy service call from a plumber with the associated visual trauma — when a plumber is bent over working under your sink, there are just some things you can’t un-see…

Did This Work For You? Tell Me About It!

If this procedure helped you get your instant hot water flowing again, make yourself a celebratory batch of instant hot chocolate, then tell me about it in the comments below!

  • Michael

    This procedure worked perfectly. My wife is now a very happy camper. Thank you so much.

  • liza

    thank you for the clear pictures and easy-to-follow instructions. did this in 10 minutes. pretty satisfying to see all the deposits coming out. my husband did not want me to do this, thinking i would mess it up and we’d have to call a plumber, but i knew it could be done w/o a hitch.

    thanks for blogging on this!

    • DIY victory always tastes just a bit sweeter when someone things we can’t do it. 🙂 Good job avoiding the plumber and making your hubby eat his words… but at least he could wash them down with a hot cup of instant cocoa. 🙂

  • Dale Ott

    Great Job Steve!!! thanks worked just as you said, I am so glad I do not have to call a plumber. Bad View, Bad Bill, $ saved. My hat is off to you thank you.

  • Chrissy

    Thank you, thank you! We live in an area where the water is very hard, so lots of build up. I am a tea drinker so my dispenser gets a lot of use.

    My hubby is not a Mr. Fix-It kind of guy by any means. These kind of tasks always seem to fall on my shoulders. I found your website and love your pictures and step by step information. I hope I can fix my sputtering, low flow hot water dispense and not have to call our handyman. I love the idea of saving $$. Glad you mentioned not using CLR (funny guy!) as this question was running through my mind. (Do you think vinegar would be OK to use?)

    • Vinegar is fine – just flush WELL! 🙂

      • Larry

        White vinegar is the standard. Very effective against Calcium Carbonate (hard water cause) deposits. Use it on Shower heads, kitchen sink nozzles, coffee makers, etc.
        An inline filter on the supply line will get rid of most of the debris that cause off tasting water. The inline filter will have little effect on the Calcium Carbonate since the mineral is in suspension in the water and “plates” out as it flows thorough the system, especially where there is a change of temperature or constriction in the water course. Good work Steve.

        Larry in Virginia

  • June Finlay

    Hi there …I have just had one of these installed and the waterflow is very slow, my plumber can’t figure it out. Its brand new so surely can’t be the build up of deposits…any clues anyone?

    Thank you


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  • fred james

    thanks for all the tips.
    i now have a problem with the thumb press connector on the inlet side, it’s leaking.

    Help !

    • Hmm…. probably cheapest just to get a new connector from Insinkerator. There’s not much inside that connector that you can fiddle with. 🙁

  • C. J. Piros

    A Mountain Products instant hot/cold water dispenser is in the house which we purchased last year. Flow is good, but we have stopped using it due to the particulate that comes along with the water. Will this draining and flushing solve this as well, do you think?

    • Not sure, but it won’t hurt! They all operate in a similar fashion, so it’s worth a shot!

      • chuck

        I am thinking of installing an in line filter to help reduce this issue. Any suggestions? Type, location etc.

        • Calcium deposits are hard to filter out completely. Any filtration method will make things better, but you should still periodically flush out any tanks in your house (including your full-sized hot water heater tank). I use a simple inline cartridge filter system in my house, just downstream from the shutoff, and I change the filter every 6 months.

          • chuck

            Just a follow up. Cause of low flow and air in system was bad internal back flow check ball. I called InSinkErator back and this time they replaced the entire unit for free eventhough I was out of warranty. I got the impression mine was one of many of this type of failure.

  • MaryCath

    They just replaced my leaking tank with a 65% discount. Much cheaper than Home Depot. The new one comes with a filter. Any suggestions of what I should do with that? I got a $75 installation fee estimate.

    • Yep! Use the filter! It should just be inline, and you can totally install it yourself!

  • Excellent write up, thanks so much for writing this. I’ll just add a cautionary tale as I followed your instructions to the letter, flushed the entire unit…. and it made no difference whatsoever! After scratching my head I went to the wall valve and discovered that it wasn’t fully turned on! Just a few turns and everything was working better than before. Just goes to show that you really do need to check ‘the obvious stuff’ first before doing the heavy lifting….

    • Glad to know it was something simple and that you got it working! Flushing it out is never a bad idea — and you probably lengthened the service life of the unit by doing it anyway. 🙂

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  • Dale Neese

    I just did the 3 fill and flush of my tank and removed a lot of sediment. I’ve connected everything back up. Turned the leaver back on and water still comes out very slowly. Removed the tip and cleaned the screen. Without the screen nozzle tip on water only comes out the little holes on the side. I’ve used a pipe cleaner up inside the faucet, cleaned the screen completely clean but water only comes out the little holes. What’s up?

  • Dale Neese

    Some tanks might need just three flushes. Some tanks will take 6-8 times or more as my tank was really clogged with calcium “nuggets” from highly alkaline well water. The water flow kept getting progressively better with each flush until the flow was back to normal. Now I will make the flushing of the tank a part of routine maintenance when I change the filters on my well water. Thanks!

  • Alex

    Wow, your suggestions worked perfect for me. I did find that I had to use a bit of white vinegar and a very small wire to loosen some deposits on the water inlet of the tank it self. Apparently I had some very tough deposits that were harden on. Wow, what a difference that made. The instant hot water works like NEW. I’m printing out your suggestions and keeping them handy should this happen again. Thanks so much. Alex.

    • David Williams

      Alex – did you find that the deposits had significantly narrowed the inlet? Mine seems to have only about 1mm clear!

  • David Williams

    Steve, thanks very much. I flushed the tank 7 times but, sadly, no improvement, despite finding a small beach in there!
    Looking at the blue pipe inlet, the diameter appeared to be about 3mm, but there was a hole of only 1 mm in the middle.
    I couldn’t tell if it was designed that way or just solid Calcium buildup.
    Do you happen to have a photo of how the inlet should look?

  • David Williams

    Sreve – you rock. I came for the Insinkerator and stayed for the F40 story.
    You are the leader and the monster of our streets.

  • David Williams

    By the way, I strongly endorse Steve’s comments on letting the water cool.
    I also advise not checking if any inlets are blocked by blowing in the cold water inlet.
    If you do, you’ll note that the vent outlet is perfectly-placed to spray hot water onto your cheek. No visit to the emergency room needed as I’d let it cool for 2 hours, but I had to pretend to my wife that it hurt less than it did!

    • Yikes. I learned a long time ago dealing with my full-size water heater just to shut it off and wait a while until I start tinkering. Faking pain management for the boss lady is never fun.

  • Doug

    We may have reached the end of the line as far as flushing the tank ourselves. Our SST tank was installed in 2006 and replaced for free with a SSRV tank in Feb 2012. The SSRV tank does not have a drain plug. I called InSinkerator and they said I’d have to buy a replacement tank (HWT-F1000S) which comes with a filter which should extend the life of the tank according to their rep (Brian). The new tank goes for $235 on Amazon. Does anyone know if the new tank comes with a drain plug?

  • Thanks… BUT.

    In my case… I took the whole thing apart to FIND… it was the pressure switch on the hot water tap itself. It had loosened enough to make the switch not function. So thanks for the instructions but perhaps amend the post to include… test the pressure switch if your unit has threaded access to the two taps on top.

    Cheers, Alex

  • Joanne MacInnes

    Where is this pressure switch? I’ve cleaned my tank twice following steves instructions with no improvement at all. Also I can’t find a way of filling the tank between each flush between each flush without it filling up with boiling water. Could the slowness be due to air bubbles and if so how do I get those out? All help and advise grateful received. Cheers, Joanne

    • David Williams

      Just cut the power to the pump so that it refills with cold water. My low pressure was caused by a faulty spring in the tap (faucet) which was replaced for £90 (about $145) including fitting. All the best!

  • Wendy Black

    Oh my goodness, what a lot came out of the tank. We had a much bigger mess in our sink Steve and thanks for the very clear instructions. Flushed the tank about 6 times and then felt that we’d got most of it out. Water flow better but we haven’t managed to fix the fact that the tap dribbles every time the water heater kicks in and heats the water. No problem at any other time but we know we have to have a jug under it when it heats up the water. Any ideas?

  • AlanPrangnell

    I discovered my sinkerator hot water unit was leaking when we saw water on the kitchen floor.
    I wanted to find cause of leak and after trial and error found it was leaking from the joint between the top and bottom part of the tank. I seperated the tank and have cleaned out about 1 inch of crud. I now need a new rubber seal. Any ideas where I can get one? Thanks

    • Have you checked with Insinkerator parts department? Is it a specially shaped seal, or just a rubber o-ring? If it’s nothing fancy, I bet you could just get one from a hardware store.

  • CJ

    I unplugged my instant hot unit before we went on vacation for 3 weeks. It had been working quite well. I re-plugged it in yesterday, and it didn’t heat up; cold water came out of the faucet. I could not hear the heater in the unit (usually hear it go on and off). Any suggestions?

    • Any chance you tripped the GFI breaker while unplugging or plugging back in? I’d test the outlet to make sure it’s powered, before checking anything else.

  • Alex Polinsky

    I tried to clean it per your instruction and of course lots of curd came out. However when I refilled it it leaked. How do I take it apart to repair the gasket?


    • alan prangnell

      I have just repaired my insinkaerator which was leaking.
      1. carefully remove the pop rivet holding he two halves of the casing
      2. gently pull off the temp dial
      3. separate the casing but be careful of the wires to the indicator light. the light will push out of the outer casing you will then be presented with the insulated water unit.
      At this point, make a note of where and how everything fits and be careful not to damage the printed circuit board.
      4. when you start to remove the insulation you will also have to remove the plastic expansion vessel
      5. FIRST PROBLEM: when you have the bare water container you will see that the two halves are bolted together with TORX bolts .(well, mine was.) when you get it unbolted, and note where the earth wire fits, gently prise the two halves apart and should find a thin rubber type gasket.
      6. SECOND PROBLEM: there is no replacement gasket listed or available from any of the sources I tried.
      After thoroughly cleaning the mating surfaces I used a silicon type gasket sealant which I use for my motor cycles. I used this in preference to ordinary silicon sealant because if it is ok for the temp that bike parts reach, it should be ok for the hot water tank. If you are not familiar with his product make sure you read the instructions.The first time I did not use sufficient and it still leaked so I had to go through the whole process again.
      7. Re assemble the unit making sure you have attached the earth wire .

      Mine has been trouble free for 2 months.

      Hope this is helpful to anyone with the same problem.


  • Ray

    Thanks Steve for taking the time to document the process. Much appreciated. Ray

  • Paul Shea

    I have insinkerater hot water dispenser ,Keeps tripping my groundfault breaker,this has just started ,what do you think is problem

  • David K

    I am stuck, My slow flow is coming from the cold and hot sides. I followed your suggestion and attempted to clean out the hot unit. see the cold and hot intake picture. I tried The screw on the bottom to empty, but it stripped. was able to empty the unit by turning it upside down, this is my second unit, the first went bad 5+ years ago by a faulty ball in the handle. I swore I would never let a stupid little ball force me to replace a whole unit. But, they now have a special key to open it. I tried all my shapes and sizes and it won’t open to allow me to change it. arggghhhhh any suggestions. Can I send you pictures?

    • I’d love to see a pic. Can you upload it to and paste the link here?

  • Sam Curtis

    Our hot water dispenser (installed 2008) started spitting and mixing air with the hot water so I did a drain and flush pretty much as described in the article, got more than half a cup of mineral powder out of it; incredible. Discovered it had been leaking under the sink without our knowledge. After pricing a new unit I decided to fix this one. Disassembled and found that the flat plastic tank on top (vent tube) has a valve type thing protruding downward that looks like the end of a turkey baster with a plastic tube attached. This sits right up against the metal tank, and heat had caused the thing to crack and develop a small hole. The water leak had rusted most of the screws holding the halves of the tank together along with the clip that holds the thermostat (temp knob) as well as disintegrating the spring clip on one end of the plastic tube. Drilled out the rusty screws, checked the inside of the tank and saw the flush had gotten all the debris out; reassembled with nine #6 stainless steel screws and nuts and some Loctite GO2 Gel on the gasket area. Also used the GO2 Gel to plug the hole and seal the crack on the plastic vent tank turkey baster end and then wrapped it with E-Z Fuse silicon hose repair tape (rated to 500 degrees F). Used zip ties on the plastic tube connection and some perforated steel strapping to hold the thermostat in place. Works great, good as new.

    • Awesome, Sam. And thank you for the detailed description of your fix. Let’s hope it helps out someone else! 🙂

  • Bethany

    I’m so happy I found your instructions. Our dispenser just stopped working all of a sudden and I thought for sure I’d be replacing it. My husband told me not to mess with it and we could hire his buddy to fix it. I don’t listen well :-). He was so impressed when I got it going again! Thanks for helping me make him eat his words!

    • Yeah, Bethany! It’s always delicious to make others eat their words. LOL. 🙂

  • Geoffrey

    Hi Steve

    Very informative article

    My insinkerator is making “knocking” noises and sometimes water is coming out when the tap is off.
    It’s about 4 years old and I live in a hard water area.
    Could the cause be a build up of limescale? If so I’m thinking of descaling the boiler using citric acid, which is lemon juice and non-toxic
    I’d appreciate your thoughts and/or comments on this



    • Hi, Geoffrey. I’d guess that’s water boiling inside the unit. Try turning down the temperature dial. I have mine set at around the 11 o’clock position. After changing the setting, let it be for about an hour and see if the water is still coming out hot enough while not boiling over. Tinker until you find the sweet spot. 🙂

  • Jacki

    Thanks for this post – worked like a charm and I’m excited for a hot cup of tea shortly!

  • lisa

    I followed your instructions and got loads of stuff out, did it 6 or 7 times, filled it back up with cold water then switched the power back on and it just keeps tripping all the electricity in the house. Any advice? Thanks

    • Hi, Lisa. That’s very strange, but the only thing I can think of is that during the flush some water got into the wiring, and is causing a short?

  • Simon

    HI, I have the following issue with my insinkerator. The water is just not hot enough when coming out of the hot tap (even when the tank is set to maximum heat). However if you look at the picture ( you will see the water coming out of the tap when the hot is switched on. The water flow on the left is actually cold water and the main flow on the right is piping hot. This is then mixing in my cup and producing luke warm water. I have replaced the whole tap with a new one but the same issue is happening so now i need to look at the tank.

    I have flushed the tank twice and got loads of the sand deposits out but still i have this issue. Any help would be much appreciated.

    You will also see the water leaks out of the top of the tap outlet when the hot is switched on. The cold is perfect and flows very well.

    • Hi, Simon. Sorry to hear that. I’ve never used one of the hot/cold units, so I’m not sure what the issue would be. If you’ve replaced the tap, then the issue must be somewhere at the tank (which doesn’t surprise me). I wish I could be of more help, but since I’m not familiar with how that tank works different as opposed to the hot-only tank, I’d just be guessing. Have you tried calling Insinkerator’s customer service?

  • my comments keep getting deleted?

    • Hi, Simon. I moderate comments to avoid spam, so sometimes it takes me a day or two to approve pending comments. But don’t worry, they’re not lost. 🙂

  • Dominique Marie Hughes

    what makes the water come out is it pressure from the water line or is there a pump in the module?
    the module is still hot with no flow..

    • There’s no pump, so the house’s water pressure is what pushes the water through the tank when you turn on the faucet.