How to de-scale a water heater, hot water geyser, water cylinder, etc:

This article describes in complete detail the steps in the procedure to remove scale or lime from a hot water heater tank - hot water heater de-scaling or de-liming procedural steps.

How to Remove Lime or Scale from a Hot Water Heater

Lime or scale in plumbing systems is caused by hard water as well as silicates, sulfates, and similar materials form water scale that coats the bottom of a hot water tank or the surface of the electrodes in an electric water heater, interfering with proper water heater operation, causing water heater noises, reduction in hot water quantity, increased water heater operating costs, and a shorter water heater life.

Silt and soil debris can also collect in a water heater tank where it can cause similar problems even if the water supply is not hard.

Silt and debris can be easily removed from a hot water tank by periodic flushing. In fact if your water heater is quite noisy, it will probably be easier to remove un-wanted mineral deposits from the water tank than it will be later if you wait until the heater is no longer making much noise (because the mineral layer has solidified).

Install a sediment filter on the incoming water supply to avoid this problem in the first place.

But lime or water scale are more difficult to remove from a water heater: manually scraping the tank bottom through the drain opening or use of a de-limer chemical will be needed. Below we describe these procedures.

Readers should also see our discussion of mineral clogging of water piping, water heaters, and tankless coils, organized

at HOT WATER IMPROVEMENTS.

Other gas fired water heater noises are discussed at GAS FLAME & NOISE DEFECTS.

• To drain your water heater tank, for example to replace a part,
  
  see WATER HEATER DRAIN PROCEDURE.
• To flush accumulated crud or debris from a water heater (yearly maintenance)
  
  see WATER HEATER FLUSH PROCEDURE
• To de-scale or de-lime your hot water heater,
  
  see WATER HEATER SCALE DE-LIMING PROCEDURE
• To diagnose and repair a bad water heater dip tube or anode,
  
  see WATER HEATER ANODES, DIP TUBES
• To diagnose particulate debris in the building water supply, faucet strainers, etc. that comes from the hot water tank, and how to fix that problem,
  
  see WATER HEATER DEBRIS FLUSH

The articles at this website will answer most questions about diagnosing and curing noisy domestic water heaters and about the procedure to remove mineral deposits, lime, water scale, silicates, sulfates, aluminates, or silt and sand from a water heater tank.

• If your hot water source is from a tankless coil, or if you suspect that the clogging problem in your building is in the piping itself,
  
  see CLOGGED PIPING & Hot Water Flow.

Why do we need to remove lime or scale from a water heater?

At WATER HEATER NOISE DIAGNOSIS, CURE we explain how scale in a water heater can reduce the quantity of hot water, reduce water heater life, and cause water heater noises. We explain why it is important to remove the scale from a hot water heater.

Step 1: Flush the Hot Water Tank to Remove Silt & Debris

The first step in curing water heater noises or poor hot water quantity is to turn off and flush out the water heater.

See WATER HEATER FLUSH PROCEDURE for the full article on the detailed procedure for draining and flushing out water heaters to remove scale, dirt, or debris - a first step in cleaning a water heater to increase hot water quantity, temperature, and water heater life, and to stop water heater noises.

Watch Out: Safety Warnings: don't tackle this water heater cleanout project on a Sunday night when you can't call a plumber or buy a replacement part. Water heaters, their heating source (oil or gas burner or electricity or solar hot water), and particularly their relief valves include critical safety components.

Do not modify or remove relief valves, chimney connections, draft hoods, etc. as you may create dangerous conditions. Turn off all electrical and or gas power to the water heater and let it cool.

This means turning off electricity that controls the water heater oil burner or electric heating elements, or for gas fired water heaters, turning off the gas supply to the device.

Additional tips on draining a water heater tank can be found

at ELECTRIC WATER HEATERS

Step 2 - Remove Scale Deposits from a Water Heater Tank - Scraping the Bottom of the Hot Water Tank

Draining and flushing the water heater without taking more steps to loosen and remove scale from the water heater bottom may be only marginally effective at stopping water heater noise and removing debris.

If there are thick, hard mineral deposits in the bottom of the hot water tank it may be necessary to take a more aggressive approach:

1. Turn off and drain the hot water heater as described in detail above
2. Remove the hot water heater drain valve (buy a new replacement valve if your old one is damaged)
3. Use a stiff wire such as a coat hanger to scrape and loosen debris from bottom of the heater. Scraping the water heater tank bottom is an alternative to using a professional deliming kit which we describe
   
   below at DE-LIMING USING SCALE REMOVERS
4. Intermittently flush the water heater into a bucket by opening the cold water supply valve into the water heater
5. Continue this water heater cleanout process until you are no longer able to remove any debris
6. Replace the water heater tank drain valve and the temperature relief safety valve if you removed it earlier
7. Re-fill the water heater slowly as we described above.
8. Check the water heater and all fittings for leaks, flush all air out of the system as we described in detail above
9. Turn the water heater back on.
10. Check the system for leaks again, including after the water tank is hot

Safety Warning: never turn on a water heater's heat source before the hot water tank has been re-filled. Otherwise you may damage the heater or create a dangerous condition.

Be sure the water heater pressure and temperature relief valve is properly installed and is the proper type.

See RELIEF VALVES - TP VALVES.

How to Use Scale Removers to Clean a Hot Water Tank or to Clean Scale from the Electric Water Heater Electrodes: Chemical Methods

Currently there are products such as UN-Lime® (a professional non-muriatic food-grade phosphoric acid based chemical de-limer intended for removing scale from water heaters, recommended by A.O. Smith, available in 1 gal. or 5 gal. containers) or possibly other acid-based products that can dissolve mineral or lime deposits in a hot water tank.

Our opinion (feedback is invited) is that using a de-scaling chemical other than one intended for water heaters or other than one specifically recommended by the water heater manufacturer would be a potentially dangerous approach for a water heater for several reasons:

• Acid etching of a water heater tank may cause hidden damage and weakening of the tank itself
• One is exposed to possible acid burns during cleanout, given the sloppy way we need to drain at the tank drain valve opening
• There is a risk of leaving acid in the water system if you do not flush it adequately

We suggest suggest dislodging as much water heater tank bottom crud as possible, but also taking a gentle approach so as to avoid even the slightest possibility of damage to the tank.

If you elect to use a deliming chemical in your hot water tank be sure to follow the manufacturer's instructions, including these general steps:

• Safety Warning
  
  Use of any de-liming product that comes in contact with the sacrificial anode of a water heater can lead to production of an explosive gas.
  
  Some large (125g and more) vertical commercial water heaters include a sacrificial anode in the tank bottom. (Sacrificial anodes are intended to reduce tank corrosion.)
• Turn off and drain 
  
  at the water heater tank as described above
• Use a standpipe 
  
  (simple 3/4" N.P.T. plastic PVC or CPBC Sch. 80 plumbing fittings & teflon tape or pipe dope including a short nipple, ell or tee, and standpipe of sufficient height to provide a way to pour in the delimer at the hot water tank drain opening) or
  
  a de-limer installation kit 
  
  provided by the manufacturer to place the deliming solution only in the bottom of the tank. The "kit" may simply be a connector that joins the container of de-limer by a hose to the water tank drain valve so that by lifting the container higher than the tank drain valve, de-limer flows into the water tank; the delimer later is drained out of the water tank back into the delimer container.
  
  Watch out:  cleaning and de-liming chemicals such as rust or lime removers can be dangerous if not used according to the manufacturer's instructions.
  
  See Lime Out / Lime Out Extra, lime remover MSDS, a Summit Brands product and
  
  see Super Iron Out, MSDS Material Data Safety Sheet rust and stain remover, also from Summit Brands.
• Do not smoke 
  
  or have sparks or open flame nearby during deliming - explosive or flammable gases may be produced.
• Do not let delimer chemicals come in contact 
  
  with skin, eyes, etc - dangerous burns can result. Delimers should be treated as dangerous chemicals. Use safety goggles, gloves, etc.
• Use the proper quantity of deliming solution 
  
  which depends on your water heater size. A table of quantity versus tank size is provided by the water heater manufacturer or the de-liming product manufacturer. For example, a 30 gallon water heater uses 2 gallons of delimer and a 30-66 gallon water heater can use 3 gallons of de-limer.
• Flush the hot water tank
  
  After the delimer has been used and drained from the water tank, you'll need to flush the tank with clean water - typically for ten minutes. (See the instructions provided by the delimer manufacturer).
• Return the hot water heater to operation: bleeding air, replacing relief valve, etc
  
  Continue with the steps we described in detail above

Delimer disposal note: if the delimer is draining into a sump pit be sure to run enough water to cycle the sump pump several times to flush that component out as well - leaving acid and debris from the hot water cleanout in the sump pump could damage it.

Don't Over-Do Acid or Scale Removing Chemicals

In Krappe's 1940 experiments muriatic acid (HCL) and hexametaphosphate solution were discussed for non-mechanical efforts to reduce or dissolve scale in piping, tankless coils, side-arm heaters, water heaters. The author reported that when the zinc coating is removed by acid (older galvanized steel water heating equipment and tanks), rusty water problems were likely.

For this reason, in the 1940's mechanical scale removal was preferred. Modern water heater tanks may be glass lined and less vulnerable to these problems.

Muriatic acid is much less harmful to copper-nickel or copper-silicone surfaces than it is to iron and steel, provided it is not left in metal contact longer than necessary to remove the scale. The message: don't over-do it: more and longer is not necessarily "better".

How to Remove Lime and Mineral Scale from A Tankless Coil

Krappe described using an acid-resistant pump and tubing connected to fittings to circulate an acid-wash through scale-clogged copper piping back in 1940. Plumbers still use this method today. The apparatus must be designed to let the scale particles and gases escape. Plumbers may simply use an acid-proof pony pump and fittings to cycle the acid wash using a plastic bucket as the receiving sump.

Watch out: this is a dangerous procedure risking acid burns or other hazards. Don't try this procedure if you are not trained and equipped to do so.

See LIME OUT / Lime Out Extra, lime remover MSDS, [PDF] a Summit Brands product.

But we have been informed by some plumbers that using acids to clean a tankless coil leave the coil internal surfaces etched and that the result can be faster scale formation than previously.

A detailed procedure for cleaning lime and scale clogged tankless coils, also suitable for some other piping and coil type water heaters is found

at CLOGGED TANKLESS COIL & HOT WATER FLOW.

How to Remove Lime and Mineral Scale from an Electric Water Heater's Heating Electrodes

Electric water heaters use one or two electrodes inserted into the bottom and top of the hot water tank. Controlled by a thermostat that senses water temperature inside the hot water tank, the electrodes are turned on to heat water inside the water tank.

On some electric water heater models (Rheem for example) the top heating unit is called the "Booster" and operates only during periods of high demand for hot water. Wiring and controls on the water heater may on some models ensure that only one of the heating elements operates at a time.

Our photo (left) shows a small electric water heater with two heating electrodes - one is located behind each of the dark access panels on the front of the heater.

• Turn off all electrical power 
  
  to the water heater and drain the hot water tank as we've described in detail above.
• Remove the upper and lower water heating electrodes 
  
  and inspect each for lime or scale build-up (or other visible damage)
• Clean the scale from the water tank heating electrodes. Soaking the electrodes in vinegar may be sufficient, or you'll need to use a professional de-liming product.
• Replace the electric water heater electrodes 
  
  you may want to test each electrode for proper function before replacing it, or if the electrode is visibly damaged, simply buy and install a new one of the same wattage and length.
• Re-fill the hot water heater tank 
  
  slowly, as we described above, including the steps to remove air from the system before electricity to the water heater is turned back on.
• Watch out: Never turn on an electric water heater that has not been filled 
  
  completely with water with all air removed from the system - doing otherwise is likely to burn-out the heating electrode(s) and could be unsafe.
• Check the hot water tank for leaks 
  
  and repair any that are found before turning on the water heater.

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Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

On 2021-03-06 by neal

how to clean scale from rv water heater with aluminum tank? thanks

On 2021-03-06 - by (mod) -

@neal,

To de-scale or de-lime your hot water heater, see WATER HEATER SCALE DE-LIMING PROCEDURE
https://inspectapedia.com/plumbing/Water_Heater_Scale_Removal.php

described above on this page;

It's always best to start with the least-aggressive cleaner and thus the safest, such as vinegar.

let me know if that leaves you with any questions.

On 2017-03-21 by Nancy

We just recently installed a stainless steel water heater (two months ago) and already having trouble with scale accumulating on the heating coils despite having a electric scale remover. We don't want to use a water softener that uses salt. What are some possible solutions?

On 2017-03-22 - by (mod) -

Sure, Nancy, please see https://inspectapedia.com/plumbing/Water_Softener_Alternatives.php OTHER WATER SOFTENING METHODS

 

Question: flush noisy water heater with swimming pool muriatic acid?

(Feb 22, 2016) Donald Diltz said:
Can I pore Swimming Pool Muratic Acid in Tank and let Sit for one or Two Hrs to desove Lime, and Then Flush?

(Feb 22, 2016) Anonymous said:
I used to Flush Steam Boilers With Acid With a Circulating Pump for 8 to 10 hrs to Get Rid Of Scal. CAme
Out Shinning as a New Penny. These were 5 Pound Boilers. 55 Years Ago.

Reply:

Anon

Please see the details including safety concerns including acid products in the article above

at WATER HEATER SCALE DE-LIMING PROCEDURE (the live link for the article in the Recommended Articles list below) for the detailed procedure for removing lime and water heater scale.

On 2016-04-14 by Dbear

Are flushing chemicals Septic safe ?

Are the gas water heater flushing chemicals Septic safe ?

Are the chemicals Septic safe ?

On 2016-04-14 - by (mod) -

DB

I think the safety of any cleaning chemicals depends on volume and concentration; If I were using a cleaner in a water heater or geyser tank I'd prefer not to send such waste into a septic system, and it shouldn't be necessary.

2015-10-05 by sunpays4@hotmail.com

Chemical removal of Lime in my solar geaser

2015-10-05 - by (mod) -

Yes you can use lime or de-scaling treatments; do your solar geyser manufacturer or instructions say otherwise?

 

Oil fired water heater takes longer to come on

I have a oil-fired water heater,it is taking longer before it come on,so the temperature of the water is alot colder than it should be. Thermostat is set where it should be. What's the cause? - Anon 10/4/12

Reply:

Anon,

Check for scale in the water heater or just clean and de-scale it. Scale acts as an insulator and so can delay both temperature sensing and increase water heat-up time.

We had this problem on a gas fired water heater; the result was that too often the water was tepid to cool when it should have been kept hot. We discussed that problem in our

article TANKLESS WATER HEATER INSTALLATION - but you don't have to replace the whole heater to fix this trouble.

A solution is to remove and de-scale the temperature sensor and control, but for safety and reliability it may make more sense to just replace the control or at least its temperature sensing component.

 

Question: Does mineral buildup inside a water heater cause the resulting hot water to be even harder due to dissolved minerals?

Does mineral buildup inside a water heater cause the resulting hot water to be even harder due to dissolved minerals? I have noticed problems with difficult to remove scale in my shower and, more importantly, my hair will not behave! (seriously) It is a 40 gallon tank, and as a single person who does very little laundry (uniforms are laundered and provided by employer) and doesn't run the dishwasher often, I'm wonderng if I simply don't turn that 40 gallons over quickly enough? Perhaps an on-demand heater would be better for me? Thank you for the article. - Judy 9/13/11

Reply:

Judy
A short answer to the question - it's possible but unlikely. Mineral deposits in a heater form as incoming water, bearing dissolved minerals, is heated, speeding precipitation of mineral salts.

Consider a heating boiler, not a water heater for a point of comparison. In a heating boiler the same physical quantity of water that entered the boiler remains therein - it is not consumed and little or no new water enters the system. In that case the amount of mineral salts available to form a precipitate or deposit is fixed, and small. And we do not normally see a problem with mineral deposits in heating boilers as a result.

In contrast, still using home heating boilers, a steam boiler does consume water at every heating cycle, and as new water enters that boiler constantly, the available mineral molecules to be deposited and accumulated inside the boiler can be significant, especially when the water supply is high in mineral content.

A home water heater in active use is operating like a steam boiler when occupants are using up hot water. When no one is using any hot water, no new cold water enters the tank, so no mineral deposition stops.

Your question asks if we see the opposite reaction, dissolving minerals back out into the static water in the heater. I doubt that there is a significant back reaction - we don't see mineral deposits easily dissolving back into the water as er do not see water scale deposits disappearing on their own.

More technically, we want to ask at what concentration of dissolved minerals in a static (no water leaving nor entering) water heater will we see back dissolving of existing deposits into the water. It depends too on heater temperatures and the water chemistry. I'll look further at the reaction and comment further.

I add that an on demand heater too can have serious trouble with clogging if the incoming water is high in minerals. You would be better off installing a water softener.

...

Continue reading  at WATER HEATER SCALE PREVENTION or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Recommended Articles

• CLOGGED SUPPLY PIPES, DIAGNOSIS
• CLOGGED SUPPLY PIPES, REPAIR
• CLOGGED TANKLESS COIL or PIPES, LIME SCALE
• HOT WATER PRESSURE IMPROVEMENT
• WATER HEATER FLUSH PROCEDURE
• WATER HEATER SCALE DE-LIMING PROCEDURE
• WATER HEATER SCALE PREVENTION
• WATER PRESSURE MEASUREMENT - what is the dynamic or static water pressure in a water supply system of faucets, fixtures, pipes, tanks, pumps, meters, pressure regulators?
• WATER SOFTENERS & CONDITIONERS for suggestions about dealing with hard water in buildings.
• WATER SUPPLY PIPE DIAMETER vs FLOW

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