Guide to Hot Water Heater Noise Diagnosis
Water Heater banging, popping, rumbling sound diagnosis & cure
NOISE, WATER HEATER - CONTENTS: Water heater noise troubleshooting & repair. How to diagnose and cure water heater rumbling, clanking, cracking, resonant shrieking or whistling, or other hot water heater noises. Advice and photo-guide to de-liming and de-scaling hot water heaters - Scale formation in water heaters and methods of prevention. How to remove silt or debris from the hot water heater tank. Rate of deposition of lime and scale in plumbing systems
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Catalog of causes & cures of noises heard at or in water heaters, calorifiers, cylinders:
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.
The sketch at page top is courtesy of Carson Dunlop Associates, a Toronto home inspection & home inspection education company. Used with permission.
Thermal-expansion water heater start-up bangs: if the water heater was cold, for example because it had been turned off or because you first used up all hot water and then stopped running water, thermal expansion might cause a water expansion problem, though I don't commonly see this as causing a "bang" - some reports claim it might. Your hot water system may need the addition of an expansion tank.
Watch out: water hammer is more than a troubling noise, it can be dangerous in subtle ways. Water hammer is usually caused by the combination of velocity of running water and the sudden closing of a valve through which water was moving. Water hammer from any source can, however cause leaks at relief valves and rarely, other plumbing leaks. A leaky relief valve can in turn become clogged by mineral deposits rendering it inoperable. That in turn can cause a dangerous BLEVE Explosion.
Gas or oil-fired water heater start-up bangs: Water heater start-up bangs can be caused by other problems including thermal expansion of metal parts, even a flue vent connector or the water heater tank itself, or more serious, water heater start-up exploding sounds may be caused by dangerous burner or fuel system problems or leaks.
If your water heater makes a banging sound only when it starts AND if your water heater is gas or oil fired the situation may be dangerous. If there is un-burned gas or oil that is being re-ignited when a burner starts then your heater is not operating properly and it is unsafe. The risk is a dangerous gas explosion or an oil burner puffback explosion.
Turn off water heaters that are making these explosion sound, bangs or booms and call for professional repair.
See GAS LEAK DETECTION, LP / NG if there is gas accumulating that is igniting and causing a boom or bang when your gas fired water heater starts-up
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.
Buzzing noises at a gas regulator on water heaters or other appliances may be due to a bad regulator or control. See GAS REGULATOR NOISES
Clicking sounds in the water heater or geyser: probably thermal expansion among water heater parts or hot water distribution piping. Modest water heater clicking or tapping sounds may be considered normal if they're occurring in a heat trap installed in the hot water supply piping above / downstream from the water heater itself. The heat trap is a device intended to prevent hot water from circulating or rising in the distribution piping before there is a call for hot water by opening a tap.
Clicking noises are normal during the ignition phase of gas-fired water heaters and gas fired tankless water heaters that use electron ignition - a feature on virtually all modern tankless water heaters and most new gas fired water heaters.
Also check the routing of hot water piping: hot water pipes passing through too-tight openings may click, tap, or even squeak as the metal hot water pipes expand during hot water flow through them.
Crackling sounds at the water heater: see Banging water heaters at the top of this list. Most likely there's a scale problem in the water heater.
Crackling on an electric water heater may be caused by scale formation on the heating elements themselves while in gas and oil fired calorifiers or heaters the scale problem is probably on the bottom of the water heater tank. Thicker scale means worse banging, crackling, knocking, popping sound. The heater needs to be de-scaled.
Humming water Heater Noises:
Reader Question: height pitched humming at electric water heater
2016/08/21 Azcabin said:
Our new electric water heater (3 months old) is making a very loud high pitched humming noise, any idea why?
Reply: electric water heater element vibration?
I don't know for sure what the humming is, Az.
On a few water heater models, particularly those using a rather long heating element, water flowing across the element may cause it to vibrate and may generate a humming sound.
You can probably diagnose this cause of humming electric water heater noise by turning off water into the heater or by making sure that nobody in the building is running hot water. If no water is running through the heater and the noise stops, you've found the probable cause.
If the humming IS traced to the heating element, ask your installer to inspect the element installation; simply tightening it may stop the humming noise.
Watch out: left-unattended, a humming vibrating electric water heater element might begin to leak at its mount.
Is there a circulator on your water heating system? If so check the pump for noise.
Watch out: a failing or mis-wired electrical circuit could cause buzzing or humming - that would be unsafe.
Are you sure it's really humming and not rumbling or hissing -sounds associated with scale deposits or simply with water heating up>?
Try turning power to the heater off, wait 5 minutes, then turn it on. Let me know what you observe.
Finally: a new heater and its installation should be under warranty so it makes sense to call the installer for help.
Hissing water heater or water cylinder noises: If your water heater is an electric unit, these same mineral deposits can cause a hissing noise when the heating electrodes are operating.
For both of the noises above, start by reviewing the discussion following below and titled Why Should You Remove the Scale Deposits, Silicates, and Silt from Your Water Heater Tank?
Knocking sounds in the water heater: see Banging water heaters at the top of this list. Most likely there's a scale problem in the water heater.
Popping, banging, crackling, gurgling, ringing, rapid surging boiling water, rumbling in the water heater or calorifier: 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 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.
Rumbling sounds at the water heater: see Banging water heaters at the top of this list. Most likely there's a scale problem in the water heater.
Screeching or screaming water heater sounds: look for a partly-closed control valve at the water heater inlet or anywhere in the building piping system.
Shrieking screaming Bosch Compact MiniMAXX gas-fired tankless water heater - in addition to bangs and rattles (scale in water heaters) in 2017 we investigated and obtained repair help from Bosch for a shreiking tankless water heater installed in San Miguel de Allende. The sound was traced to a resonant frequency air or exhaust movement interacting between combustion air intake and exhaust flue outlet gases.
Two diagnostic recordings of resonant whistling or shrieking water heater sounds are given just below.
BOSCH MiniMAXX CALENTADOR de GAS Resonancia Shrieking WHISTLE NOISE vs Temperature Setting - DIAGNOSIS STEP 2 [MP4] 11MB - shown above. In this recording we show that setting the temperature up at the water heater causes loud shrieking. This Bosch heater includes a variable-speed burner and fan that induces more combustion air and increases the tankless water heater's output either when the hot water usage rate goes up in the building or when the water temperature is set to a higher level.
At the increased demand or temperature settings as air and exhaust flow through the heater speeds-up, a high-pitched resonant frequency screaming ensues. Partly covering the air intake at the top of the water heater stops the noise- confirming that the probable noise cause is right at that area of the heater.
The Bosch service technicians found and "fixed" the shrieking sound problem by a combination of re-sizing of the exhaust flue vent connector at the water heater and a partial blockage of the combustion air intake at the water heater top. [Second photo above and close-up photo below]
Watch out: don't even think of trying to fix this noise yourself. Making a mistake risks fatal carbon monoxide poisoning. Consult Bosch customer service if you are having noise problems with your tankless water heater.
Ticking sounds or tapping sounds in the water heater: see Clicking water heater sounds earlier in this list.
Relationship of Hard Water to 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 de liming 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. 
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, unnecessary 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.
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.
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.
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.
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
atBLEVE 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
More water heater noises and some recommendations are in the Residential Gas and Electric Water Heater Handbook [PDF] provided by A.O. Smith and linked-to
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.
Continue reading at WATER HEATER SCALE DE-LIMING PROCEDURE for electric water heaters or water cylinders, or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.
Questions & answers or comments about water heater noise troubleshooting and water heater scale and lime removal.
Use the "Click to Show or Hide FAQs" link just above to see recently-posted questions, comments, replies, try the search box just below, or if you prefer, post a question or comment in the Comments box below and we will respond promptly.
"Why, When & How to Remove Water Sale from Tank Type Glass-Lined Water Heaters", [PDF], A.O. Smith Water Products Company, 5621 W. 115th St., Alsip IL 60803 USA, Tel: 1-800-433-2545, Website: www.hotwater.com, Email: www.hotwater.com/parts, retrieved 15 March 2015, original source: http://www.hotwater.com/lit/training/4800r9.pdf Quoting:
"..., as the result of cleaning product developments and field testing, A. O. Smith presents a preventive maintenance
plan for residential and commercial, gas, oil and electric, tank type water heaters. ... water scale and silt
accumulations can cause dissatisfaction and element or
The amount of calcium and magnesium carbonate (lime)
released from water is in direct proportion to water
temperature and usage, see chart. The higher the water
temperature or water usage, the more lime deposits are
dropped out of the water.
Water heater warranties usually state that the tank must be
free of excessive scale or lime deposit or that heater leaks
must be due to rust, corrosion or other chemical action of
water. In other words, in most cases where heater failure
is due to dropout of water impurities, the manufacturer’s
warranty does not apply"
"Residential Gas and Electric Water Heaters: Service Handbook", PDF], A.O. Smith Water Products Company, 5621 W. 115th St., Alsip IL 60803 USA, Tel: 1-800-433-2545, Website: www.hotwater.com, Email: www.hotwater.com/parts, retrieved 15 March 2015, original source: http://www.hotwater.com/lit/training/320991-000.pdf This handbook provides service information for residential gas water heaters that are atmospherically vented and use a thermocouple as their electrical source and to residential electric water heaters having one or two heating elements and common wiring configurations for these water heater models.
Mark Cramer Inspection Services Mark Cramer, Tampa Florida, Mr. Cramer is a past president of ASHI, the American Society of Home Inspectors and is a Florida home inspector and home inspection educator. Mr. Cramer serves on the ASHI Home Inspection Standards. Contact Mark Cramer at: 727-595-4211 mark@BestTampaInspector.com
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Thanks to researcher Robyn Goldstein, Rush Manager, Information Express, 650-812-3585, email: firstname.lastname@example.org,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.
 A.O. Smith's Form No. 4800 Rev. 8 Why? When? & How? /UN•LIME Specific De liming 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 De liming Coil-Type/Tube-Type Commercial Water Heaters and Hydronic Boilers *Normally supplied when ordering Part No. 4930 Motorized De liming 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.
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