Measuring thickness of scale in water heater tank bottom (C) Daniel Friedman Hot Water Heater Tank or Electrode Lime & Scale Removal Procedure - How to De-Lime the Water Heater

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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.

We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.

How to Remove Lime or Scale from a Hot Water Heater

Water heater scale after removal (C) Daniel FriedmanLime 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.

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

Water heater being flushed (C) Daniel FriedmanDraining 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 deliming 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:

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:

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, 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 Heater (C) Daniel FriedmanElectric 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.


Continue reading at WATER HEATER SCALE PREVENTION or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.


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