Descaling a Water Heater

Descaling is an issue and there is a lot of effort involved to get the minerals out, chemicals and flushing. The mineral plating due to the heater operation is tough stuff to reverse and it takes time.

Plan on it taking time to do it sucessfully, but it is can be done if your interested. Woody

I think you need something like this:

http://www.youtube.com/watch?v=CJnlnsqluTA

The video has good points but it never tells you to unplug the pump and if you follow the actual steps youll get a face full of organic cleaner, yuckie..

Plan ahead, it takes time and you have to dry run the steps to be sure you know what it is suggesting that you do. Woody

Just use household viniger. put it into your water heater and leave it for a day. do it before you go to work. and drain it out when you get home, you will be suprised at what comes out, and you do not need any protective clothing or wory about wether all of the chemicals have been flushed through.

Happy descaling.

I agree, Vinegar will work. But also recommend Citric Acid in a 10% solution, let it soak. Repeat if necessary.

GAs to the above.

If that doesn't work, then the Original Poster might try a cheap brand of cola, which contains a fair amount of phosphoric acid.

All these three are compatible with human ingestion, of course, and that factor may influence the selection of the cleaning agent.

Heating it up is an option. The most likely off-gases from the scale are carbon dioxide, which has no smell, and sulphur/sulfur dioxide and trioxide, which have a pungent smell. So the original poster would be well advised to do it either with the windows open, or outdoors.

<...Muriatic...hydrochloric acid...>

The metal from which the equipment is made is at severe risk of corrosion if this is used, in which case 1:1 replacement of the unit becomes the only way out.

Several posters offered good ideas to help you descale. You may want to consider what you will do after you are successful in descaling. Consider adding a sequestering agent like polyphosphate. They are available in saturation cartridge filters and can easily be installed in front of the cold water supply to the hot water heater. And they work. Under $50.00

Good Luck.

Wanna get it done and over with? My oldest son works for a plumbing company and services these units and was nice enough to show me how they do it. First off, this method only works on units made with a certain type of metal tubing. Does your heater have stainless/nickel steel pipes? Mine does. I now use a 50/50 solution of muratic pool acid,(get it at pool supply places) and used a cheap, all plastic drill pump(runs with a power or cordless drill) cheap plastic polyethylene tubes and a plastic 5 gallon bucket to circulate the acid water mix thru my heater. I only used one gallon of acid with one gallon of water mixed together in the bucket. In 2-1/2 minutes, the solution was clear, I then rinsed it out with fresh water for three minutes and reconnected it to the system. I guarantee you it's clean as new, not to mention sterile inside. Only works on stainless or nickel units. Might get away with it one to five times with copper, but it eventually eats the copper tubes up. DO NOT use it on aluminum. A hot and very violent corrosive reaction will occur. Use this method only outside in good ventilation and stand upwind, do not breathe the acid fumes. Muratic acid fumes are evil, and there will be lots of fumes. Have a hose running nearby for rinsing off with just in case you spill some on your skin. I recomend you wear gloves and safety glasses if you have never worked with muratic acid before. This is some mean stuff. It will eat concrete as well, so be sure to rinse it off if you spill any. After rinsing, put a whole regular box of Arm and Hammer baking soda into the bucket, stir it a bit, fill it the rest of the way with fresh water, and then it's safe to pour out on the grass, and then water the spot well. The whole proccess takes about 30 mins once you have all the materials (bucket, acid, tubes, drill and pump, baking soda, water hose, rubber gloves, etc)together.

Recommend refering to chemical MSDS, and wearing appropriate protective clothing before doing this.

Muratic acid (google searched it) is also known as Hydrochloric Acid. This is, at the least, dangerous to use such a strong acid to simply descale your pipes. There are many safer alternatives (such as house hold vinegar), which won't send you blind if you splash them in your eye.

The references I found of pool muratic acid said it is 10.4%, so a 50/50 solution would be 5%. A 5% Hydrochloric solution is very strong and dangerous, this will cause burns to skin if exposed, and it fumes badly (especially when reacting with Calcium carbonate, aka scale, which gives off large amounts of CO2 bubbles). The reaction is also exothermic, so may produce heat (depending on the concentrations involved). Strong acid, bubbling and hot - Please take care if using this method.

I suggest using safer alternatives to remove the scale over a few hours, rather than using highly dangerous solution to remove it in minutes.

Anthony

Muriatic acid is usually sold in 20° or 20 Baume concentration. This concentration will vary but is much higher than 10%. Usually 26 to 32% HCl is available in swimming pool muriatic acid unless it has already been cut by a reseller. Be careful on the concentration you are using to do this type of job. It can be very dangerous.

When I owned my water technology company, we were often asked to clean hot water tanks. Obviously we were reluctant. Instead we would make up a 3% solution of HCl and instruct the owner how to do the cleaning (we also told the owner that vinegar or citric would be suitable alternatives). Always we would stress caution. You must also consider the materials involved. If we were to damage a HWT we would likely have faced a replacement cost. Yes HCl is faster but the hazards were often too great to consider it. I never attempted to clean a point of use hot water dispenser but we were never in that business.

Another cleaning agent to descale wells is sulfamic acid as it is less volatile than HCl. In fact it is often included in many common descaling agents like CLR and Limeaway. It can be purchased in a granular form and mixed as needed. Slightly slower than hydrochloric acid but a heck of a lot safer. You can make it stronger than the more common household descalers or simply use these products as sold. Safety is always paramount and one needs to be wise enough to know the hazards of the products they are using.

I would also suggest a chemical analysis of the cold water supply to apply an appropriate control. I suggested polyphosphates (PP) as the saturation dispensing cartridges are readily available at low cost. PP does not remove calcium but sequester it so it will not precipitate on the component during heating. If calcium is the problem that is an easy solution.

"10.4%, so a 50/50 solution would be 5%."

pH is a log. HCl is <1.8ph> if you add 100% dilution with 7.4pH city water you're only going to move the pH up a point or two. Still highly acidic and highly dangerous.

We use HCl here and I would recommend vinegar (2.5-3pH) every time as an option as HCl is a chemical acid and highly corrosive and cytotoxic.

It is generally recommended to follow the manufacturer's recommendations for operation and maintenance not only to keep the warranty clause in tact also to keep the equipment in good working condition.

If you don't already have a pair shut off valves and pair of hose bibs between the sov's and the tankless unit.. find a way to install them.

.. if you have that.. you are almost done.

Shut off the water.

connect a couple of short hoses and get a bucket of solution.

Either siphon/suck your (vinegar) wash into the unit and let it stay in over night, or pump it through a few times..

I did not read all the blogs... but I would say to turn off your heating system, unplug, etc. before you begin servicing the unit. Carlos

You may have already investigated this action, but I will suggest it anyway.

I also have a tankless water heater that has an inlet filter which clogs with some kind of precipitated granules that accumulate in my water system. I have to clean this filter at least every 6 months or I have the same symptoms you have described. I have also performed the vinegar purge, using a transfer pump and a 5-gallon bucket. I did have a little build-up but the bigger issue for me is the filter cleaning and it is a whole lot simpler.

If you haven't already checked this, it might save you a more tedious task, especially if you do not already have the necessary bypass valves and hose connections for the purge. My guess is that your filter is the culprit.

Doog,

I suspected the filter first and when I cleaned it I had no success. I bought a new one ($7 plus $7 shipping) and that's working for the time being but I know the water pressure is down from when the unit was first installed. This is why I came to the descaling question.

Yeah, using muratic acid (like the plumbing techs do) requires common sense and proper safety gear/glasses/gloves and special handling, just like gasoline and household bleach, or the acid you buy to pour in your swimming pool. (the same "dangerous" muratic acid) Ooh, aren't you just terrified?

The plumbing companies use it because they don't have two days or more to wait with the water off while vinagar slowly eats it's way thru the calcium carbonate in the heater. Yes, it takes TWO FULL DAYS or more to clear a nearly blocked heater using such a wussy, weak solution, even with constant circulation. When you call a serviceman to clear your heater, you are paying him by the hour. They have your water turned off. They have to have an effective fix, and they need it fast. The acid treatment takes 20 mins and it's done. Go to the local pool supply, get yourself a gallon, read the directions on the bottle, use the proper precautions and safety gear, read my previous post and you'll be done with it quickly, not sitting around with your water off for two or three days trying to use vinegar.

Try " Calgon Nickel Safe" de-scaler. It fairly mild to equipment

Great for Ice Machines and silt, but terrible for hard water scale.

CALL A PLUMBER, if something goes wrong, you get a new water heater. If it goes right you get a smooth operating water heater.

Remember Murphy's Law usually prevails!

Well, being without the water is not an issue. I do have some shut off valves and can integrate a vinegar solution the next time my tenant is away traveling (it's her hot water). Now for a vinegar solution, is 10% adequate?

get a of gallon or two of the cheap stuff from the grocery store.. only dilute it if you still don't have enough to fill the pipes..

Get enough plain white vinegar (2-3 gallons), do not dilute as it will then take longer.

Isolate the coils from the domestic water and drain out all of the water.

Set up hoses and a circulating pump with a large (5 gallon) bucket as the reservoir.

Cover the bucket so the vinegar does not evaporate.

Keep the heat on.

Check it every hour and quit when the flow is full.

I have hard water, copper coils and do this about once a year without gloves.

Any question as to whether vinegar will work? Boil an egg in full strength vinegar, it will disolve the shell.

The plumber who originally installed my water heater was a money sucker and as such was never allowed into my home again. I got a reccomendation from a friend and now have a great plumber (if anyone in the Boston area wants his details, pm me).

Problem #1 with self descaling: The inlet and outlets were not open and as such the plumber had to add two taps.

Problem #2: Since I'd have had to buy parts, I felt that this way, I could see what was being done and make a decision next time.

So my plumber told me, that this would have to be every other year as buildups were common in the tankless systems and you never hear about them before buying one. He also used a biodegradable cleaner which was a nice touch in my mind. The whole operation took over an hour. My cost for parts and labor was $155. In my mind, I feel I got a good deal, and I guess that's what counts.

I work with HCl at a variety of concentrations and thought I would share what I know firsthand about it.

HCl is not scary. HF is scary, I won't go into that. H2SO4 is dangerous, Nitric is an annoyance, but HCl is the sweetheart of the mineral acids. Just don't put HCl and Nitric together unless you *really really* know what you're doing: That's called Aqua Regia, and it's back to scary. Maybe very scary.

HF even diluted will put you in the hospital for calcium gluconate injections. HCl OTOH full strength (12N) if it gets on you will make your skin itch and hurt right away, oh ow. 50% (6N) if you rinse it off you won't notice anything, 10% (1N) you could probably bathe in but don't. I've never had it bother anything but cuts. 12N does fume, and the fumes are bad news. Obviously don't get any HCl near your eyes or swallow it. Always add the acid to the water when diluting, etc.

OK. The concentration of HCl in stomach acid is about 1% (0.1N). That's the sourness when you barf. 2% tastes just like that but much much worse (don't ask me how I know that, but it was just unpleasant, not injurious).

These are some practical points of working with HCl that nobody will tell you. Don't be stupid, it can really hurt you, but it's nothing to be afraid of as long as you follow basic safety practices you learned in freshman chem. And if you haven't had a real course in chemistry go back to treating it like a vampire treats holy water.

More in a moment.

I'm going to descale a 50gal hot water heater, btw.

jon

That is always one of the funniest quotes.......a Hot Water Heater........ I have a computer Geek friend of mine loose it once he went into Logic Overload.......they are Water Heaters......................Why HEAT HOT Water.

Hugh............................

Because it's not hot enough?

Right so they would heat the water cause its cooled its no linger HOT, thus in the stores they are called water heaters.

How much HCl do you need to descale something? OK I am fallible: a Ph.D. from MIT does not protect me from being stupid. It's really all freshman chem, so please check me

Funny thing, the molecular weight of CaCO3 is 100! Sweet. And HCl is 36. And the concentration of HCl in a conc solution is 35%. When you do the dimensional analysis, it works out to wt CaCO3 = wt concentrated HCl (ie Pool Acid).

How about that? 1:1 by weight!

So for a tankless heater with a few grams of scale in it, you hardly need anything. My 50 gal heater, will need more: I took about a pound of loose scale out of it just on the last flush (first one actually, after ~7 years). Time to actually try this out in a beaker to see about dilutions and whether I got the units right. My prediction is that it won't quite all dissolve, even at exactly the right ratio.

Jon

So I dissolved about 5ml (~10g) of pipe scale granules from my water heater in HCl. The initial dilution was 5:1, 10ml muriatic at 31.5% to 50 ml water. This made a 1.4N solution that ought to fizz pretty well and produce quick results. We use 1N in our geology test kits.

Dumping the pipe scale into the 1.4N acid, it did indeed fizz like crazy, but only about half of it dissolved after 10 minutes. I let it go 1/2 hour to be sure. Putting a fresh grain of scale in did nothing, that meant that there was excess carbonate and the acid was all reacted. I added 5 ml of acid more and got a gratifying fizz up again, which subsided after about 10 minutes, with less residue, and twice more, over an hour at which point all the pipe scale was dissolved, and any fresh grains dropped in fizzed.

I poured the whole solution through a paper filter to try to see how much insoluble residue remained, but it clogged the paper. That means probably a lot of residue, but very fine grained.

Conclusions:
1) For complete dissolution you need plenty of excess acid, about 2.5:1 by weight.
2) 1.4N is too strong -- I would be worried about scaling that reaction up to a few gallons.
3) Lots of gas is evolved, but it wasn't especially noxious.
4) Insoluble residues might include hematite (rust), gypsum, and dolomite, but appear to be very fine grained, and thus easily flushed out.

Jon

I know this is an old thread, but just to give my experience. I'm just a homeowner, have a Rinnai tankless gas heater, water here is just over to the hard side, so not too bad.

Was using Flow-Aide diluted in a bucket per directions, with recirculating pump, this was recommended by installer as better than vinegar. Installer said I could go a 9 months to a year between descalings, but I decided on every 5-7 months when the time changes (I do most of my maintenance chores at the time changes as it's an easy way for me to remember). I got very little scale out at each flush, and the heater continued to work like new.

Anyway, had a plumber come out for unrelated issue, got to talking about the unit and how having to do the flush is inconvenient. He said he's had a unit for 10+ years, he put a high quality replaceable filter on the cold inlet, and didn't descale it for 10 years. He changes the filter once every year or so, takes only a few minutes and done. He decided to descale at the 10 year mark for good measure, he got very little out of it and no difference in operation. He's of the opinion it's probably not necessary to descale more often than 5-10 years unless the water is extremely hard or the filter used is not up to the job.

That sold me. I had him install the same filter on my cold water line. The filter costs a bit more than descaling a couple of times a year but zero inconvenience.

I still had some Flow-Aide left over so descaled anyway after two years of using just the filter, didn't get a thing out of it. Tiny inlet filter still clean as a whistle too.

Way to go with these units, IMHO. YMMV.

Kind regards.

<He's of the opinion it's probably not necessary to descale more often than 5-10 years unless the water is extremely hard or the filter used is not up to the job.>

Couldn't find a way to edit my post... He meant the above in the context of using the filter. Sorry for any confusion.

• Kettle descaling fluid from the local DIY store (formic acid)
• Vinegar (acetic acid)
• Lemon juice (citric acid)
• Proprietary cola [brand names withheld] (phosphoric acid)
• Etc.