Free Encyclopedia of Building & Environmental Inspection, Testing, Diagnosis, Repair

Ask a Question or Search InspectAPedia

• HOME
• AIR CONDITIONING
• ELECTRICAL
• EXTERIORS
• HEATING
• HOME INSPECTION
• INTERIORS
• PLUMBING
• ROOFING
• SEPTIC SYSTEMS
• STRUCTURE
• WATER SUPPLY

• ENERGY SAVINGS
• ENVIRONMENT
• INDOOR AIR IAQ
• INSULATION
• MOLD INSPECT TEST REMOVE
• NOISE
• ODORS
• SOLAR ENERGY
• VENTILATION
• EXPERTS DIRECTORY
• CONTACT US

This article explains how to diagnose and cure noisy water heaters such as popping, hissing, crackling or banging. We describe the different types of sounds heard at a water heater, what they mean, their cause, and their elimination.

At WATER HEATER SCALE - De-Liming Procedure we describe exactly how to get rid of water heater scale, a common cause of water heater noises. Also see WATER HEATER SCALE PREVENTION. The sketch at page top is courtesy of Carson Dunlop. For a more broad list of noises traced to heating equipment, also see HEATING SYSTEM NOISES.

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. This website contains in-depth articles on inspecting, testing, and repairing problems residential hot water heaters of all types, including their parts, controls, and alternative sources for hot water as well as tips for improving hot water temperature, hot water pressure, and hot water quantity. Reproduction of this web page electronically at other websites is prohibited.

© Copyright 2012 InspectAPedia.com, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use page top links to major topics or use links at the left of each page to navigate within topics and documents at this website. Green links show where you are in a document series or at this website.

Noise Diagnosis & Repair Guide for Residential Hot Water Heaters

If you hear loud popping, cracking, or clanking noises from your hot water heater when it is operating, the cause might be mineral deposits which have accumulated on the bottom of the water heater tank interior surface. If your water heater is an electric unit, these same mineral deposits can cause a hissing noise when the heating electrodes are operating.

If your water supply is hard (see DETECT HARD WATER), the minerals in the water tend to precipitate out at the hottest place in the plumbing system. Often this means that the water heater itself will accumulate solid precipitate of minerals.

Our photograph (left) shows our measurement of the thickness of mineral scale removed from the bottom of a six-year-old gas-fired water heater - more than 1/2 cm in thickness! The "lime" scale that forms in water heater tanks is composed principally of calcium and magnesium carbonate.

For the broad topic of controlling plumbing noises in buildings see Sound Control for Plumbing. Also see NOISE / SOUND DIAGNOSIS & CURE where we describe how to locate the source of, identify and correct various building sounds and noises indoors or on occasion, noises from outside that penetrate indoors at annoying levels. Separately at SOUND CONTROL in buildings we provide a series of detailed articles on reducing unwanted building noise levels through building design, insulation, sound isolation, and noise barriers.

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.

Hard Water and Water Heater Noises

The hard water mineral deposits tend to collect as a hard skin on the bottom of the heater, interfering with heat transfer, increasing operating cost, and over longer periods, possibly weakening the bottom of the water heater itself.

Mineral deposits also accumulate on the electrodes of an electric water heater, eventually leading to the failure of the heating electrode. If you never remove the scale from a water heater tank the clanking or cracking noise heard at the water heater during operation may eventually cease when the scale solidifies, no longer trapping hot water and interfering with its movement upwards in the water tank.

However the development of a thick lime or scale layer in the bottom of a water heater also reduces the water heater tank life.

• Water heater manufacturers recommend flushing the heater monthly to remove silt, and where water is hard, regular deliming of the water tank - steps which in our experience we see that almost no one does. With experience you may discover that flushing is required less often (or more often) in your area.
• On occasion when a heater fails (or in rare multi-defect cases, explodes), the leak and failure occur at the bottom of the tank, leading to a BLEVE explosion and a water tank that becomes a rocket.

Other Water Heater Problems Caused by Hard Water & Scale Deposits

Why Should You Remove the Scale Deposits, Silicates, and Silt from Your Water Heater Tank?

Our photo (left) shows chunks of water heater scale on the ground after removal from the water heater.

A.O. Smith gives six reasons (here we expand and add to them) for water heater tank scale removal, and the company points out that the reasons for scale removal and indeed the procedure for scale removal is (almost) the same regardless of the energy source: electric, gas, oil, solar water heaters.

Our "exception" is that solar water heaters and electric water heaters may have specific internal components (such as electric water heater electrodes) that will also need to be de-scaled or even replaced. [1]

Noisy water heater operation: Water heater noises, as we described above, may be the first thing people notice when the water tank scale layer has become thick enough to interfere with good water heater operation. But A.O. Smith and other water heater manufacturers cite additional reasons why removing water heater scale is important. Clean the water heater tank to reduce water heater noise.

Longer water heater "on" time & slower water heat-up rate: you can reduce the cost of making hot water with your oil, gas, or electric-fired water heater by removing scale from the tank bottom. The scale layer on the tank bottom (or on an electric water heater's electrodes) interferes with heat transfer into the hot water.

This means that the water heater will have to operate longer (and you will spend more on hot water costs) than necessary to re-heat incoming water. Clean your water heater tank to reduce your water heating cost by improving heat transfer into the water and correspondingly shortening the water heater "on" cycle time.

High water heater costs to operate, repair, replace: for the same reasons as above: running the water heater longer just to get the water hot enough means higher water heater operating expense. In addition to higher energy costs to heat the water, unnecesary heater replacement, and in the case of electric water heaters, early failure of the heating elements are common results of heavy scale problems.

Hot water quantity has diminished - not enough hot water: by slowing heat transfer into the hot water in the water tank, the apparent hot water quantity will also be reduced, because incoming cold water is not heated as rapidly when occupants are drawing hot water out of the tank. Thus the incoming cold more quickly dilutes and cools the hot water that remains in the tank during use. Clean the water heater tank to increase hot water quantity.

Extend the water heater life: because scale on the water heater tank bottom insulates the tank bottom from the water inside the tank, the bottom of an oil or gas fired water heater will become hotter as the scale layer gets thicker. These increased temperatures weaken the water heater tank bottom and shorten the life of the water heater. Similarly, scale deposits on the electrodes in an electric hot water heater shorten the life of the electrodes. Clean the hot water tank regularly to extend its life.

Protect water heater warranty: if a water heater tank fails the manufacturer may not honor the water heater's warranty if the failure is due to the accumulation of excessive scale inside of the water heater tank. Water heater warranties typically indicate that the tank is warranted against leaks due to rust, corrosion, or chemical action of the water but the warranty will exclude a tank failure due to scale.

User dissatisfaction with the water heater because of less hot water, slower hot water recovery, and higher hot water costs lead to unhappy building occupants who may have no idea that a water heater scale problem is the cause. If dissatisfaction leads a consumer to replace a water heater that could have just been de-scaled, there may also be unnecessary heater replacement expense.

How Often to Remove Scale Deposits from a Water Heater

When the lime thickness reaches the hot water tank drain, there will be about one inch of mineral deposit on the tank bottom. If the water tank has a cleanout opening, when the lime thickness reaches that opening the mineral deposit thickness will be about 2". When you have observed the length of time required for lime to accumulate in your water heater you can set the appropriate maintenance schedule.

How the water heater scale is removed

See WATER HEATER SCALE - De-Liming Procedure for a detailed water heater de-liming procedure. A summary of the de-scaling procedure is just below.

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 flushing out water heaters to remove scale, dirt, or debris - a step that can increase hot water quantity, temperature, and water heater life.

Watch out: 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

The second step in curing water heater noise or insufficient hot water is to remove scale or lime from the water heater tank. If the unit is an electric water heater, you'll also need to remove scale from the electric water heater elements. See WATER HEATER SCALE - De-Liming Procedure for the full article on the detailed procedure for removing lime and water heater scale.

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.

Step 3: Prevent Scale Deposits in Water Heater Tanks or on Electric Water Heater Electrodes - Scale formation in water heaters and methods of prevention

The third step in stopping water heater noises, extending water heater life and increasing the amount of hot water that the heater produces, is to prevent un-wanted scale or lime deposits in the water heater tank or on an electric water heater's electrodes. Please see Water Heater Scale Prevention for the detailed article on this procedure.

The rate of deposition of scale inside of a water heater tank depends on

• The hardness of the incoming cold water. See MEASURE WATER HARDNESS for details about how water hardness is measured.
• The temperature to which the water is being heated. Higher water temperatures cause minerals to be deposited faster than lower water temperatures.
• The water quantity used: the more water that flows through the water heater (in gallons of use per day,) the faster it will be clogged with minerals or debris.

At Water Heater Scale Prevention we discuss in detail and provide research on the factors determining the rate at which scale and lime form in water heaters or on water heater electrodes.

How Mineral Deposits and Heating May Weaken a Water Heater Tank Bottom, Contributing to BLEVE Explosion

BLEVEs or boiling liquid expanding vapor explosions are discussed at BLEVE EXPLOSIONS. Excerpts are below

Water heater tank explosions are rare thanks to the widespread requirement for and use of pressure and temperature relief safety valves. The photo (left) shows a hole in the roof made when a water heater exploded, becoming a rocket that passed up through the building.

But if the safety valve has been damaged, modified, or even omitted (as we saw on our neighbor's water heater), that condition, combined with overheating can cause a water tank to explode, creating a BLEVE - boiling liquid vapor explosion that releases tremendous force and causing extreme damage to a building.

Because repeated heating of the water tank bottom may combine with other conditions (such as corrosion or excessive heating due to mineral deposits on the tank bottom) to produce a weak water heater tank bottom, that is the part more likely to fail in an overheat and overpressure condition.

A failure at the water tank bottom may explain why a BLEVE can produce a water tank explosion that behaves like a rocket, sending the water tank skyrocketing up through a building.

Cures for Hard Water that Clogs Hot Water Tanks, Tankless Coils, and Plumbing Pipes

See WATER HEATER SCALE - De-Liming Procedure for a detailed water heater de-liming procedure.

See WATER SOFTENERS & CONDITIONERS for suggestions about dealing with hard water in buildings.

Questions & Answers regarding this article

Questions & answers about water heater noise troubleshooting and water heater scale and lime removal.

Share this Article      

...

Technical Reviewers & References

• InspectAPedia.com^® - Daniel Friedman - Publisher & Editor.
• InspectAPedia Bookstore lists recommended books, organized by topic & available for purchase. Most of our articles also list books on the specific article topic as well as other references, and information sources.
• Critique, contributions wanted: Contact Us to suggest corrections or additions to articles at this website, and if you wish, to receive online listing and credit as a contributor. Particular thanks are due to the many experts and also consumers who read and critique technical articles at InspectAPedia.com.
• Additional technical contributors & reference sources for this article are listed below.

Use links just below or at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

WATER HEATER NOISES
  Water Heater Flush Procedure
  WATER HEATER SCALE - De-Liming Procedure
  Water Heater Scale Prevention

• Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. (416) 964-9415 1-800-268-7070 info@carsondunlop.com. Thanks to Alan Carson and Bob Dunlop, for permission to use illustrations from their publication, The Illustrated Home which illustrates construction details and building components. Carson Dunlop provides home inspection education including the ASHI-adopted Home Inspection Training Program (home study course), publications such as the Home Reference Book, report writing materials including the Horizon report writer, and home inspection services. Alan Carson is a past president of ASHI, the American Society of Home Inspectors.
• Thanks to researcher Robyn Goldstein, Rush Manager, Information Express, 650-812-3585, email: service@ieonline.com,for researching the Purdue bulletin No. 74 original citation 03/2010 . Information Express supplies "... institutional document delivery needs - A full service company specializing in the fast, accurate and competitively priced delivery of published articles for all industries"
• Pounds of lime deposited vs. temperature and hot water usage: see Purdue Bulletin #74 (also provided by A.O. Smith in the article below). Purdue's chart shows the number of pounds of lime deposited per year as a function of the water usage in gallons per day, with an assumed 10 grains of water hardness.
• "When, Why, and How to Remove Water Scale from Tank Type Glass-Lined Water Heaters (for non glass-lined tanks, consult water heater manufacturer)" PDF provided by A.O. Smith Water Products Company - hotwater.com/lit/training/4800r9.pdf 800-433-2545 - 01/07/2009.
• [1] A.O. Smith's Form No. 4800 Rev. 8 Why? When? & How? /UN•LIME Specific Deliming Instructions for use with Up-N-Down Transfer Kit for Tank Type Heaters. (Normally supplied in UN-LIME shipping cartons), Supersedes Form Nos. 4800 Rev. 7 and 4813-100.
  
• A.O. Smith's Form No. 4778* All about Deliming Coil-Type/Tube-Type Commercial Water Heaters and Hydronic Boilers *Normally supplied when ordering Part No. 4930 Motorized Deliming Pump Kit
• Rheem Electric Water Heater "Owners Guide and Installation Instructions", (Australian models) rheem.com.au/images/pdf/owners_dom-elec_121996C_0707.pdf
• "Scale formation in water heaters and methods of prevention", Krappe, Justus Maximilian, Engineering experiment station. Gas engineering bulletin; no. 6; Research series; no. 74; On cover: Engineering bulletin, Purdue university. Vol. xxiv, no. 3a. June, 1940 (Layfayette Indiana) commonly referred to in some references as "Purdue University Bulletin No. 74" - thanks to researcher Robyn Goldstein for the full citation. LCCN: 40028844 & OCLC: 1038544 - Water analysis, water softening, hot-water supply. 27pages. You can obtain this document through your local library. (full copy file at InspectAPedia 3/31/2010) Purdue B074 can be hard to locate online.
  Also Bradford White Corporation (a manufacturer of water heaters) has published excerpts from that document, available at Purdue_B074_BradfordW.pdf
• Other sources of information on calculating the rate of lime deposition from hard and hot water:
  • Wilkes University Center for Environmental Quality Environmental Engineering and Earth Sciences Hardwater, Water Hardness "Hard Water Hardness Calcium Magnesium Water Corrosion Mineral Scale" http://www.water-research.net/hardness.htm
  • Chemical Engineering, Joseph D. Hagerty Editor, McGraw-Hill, 1989, ISBN 0685270831, 9780685270837
    "To calculate the amount of material that will be deposited in 1000 gal. of water per day, take the number of grains per gallon of each as shown by the ..." also difficult to obtain except as a used copy.

Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair

• Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.

• Carbon Monoxide Gas Toxicity, exposure limits, poisoning symptoms, and inspecting buildings for CO hazards
• ...