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AGE of WATER HEATERS
AIRBOUND HEAT SYSTEM REPAIR by WATER FEED VALVE
ALTERNATIVE HOT WATER SOURCES
ANODES & DIP TUBES on WATER HEATERS
ANTIFREEZE for BOILERS
ANTI SCALD VALVES
APPLIANCE DIAGNOSIS & REPAIR
APPLIANCE EFFICIENCY RATINGS
AQUASTAT CONTROL Functions
BACKDRAFTING HEATING EQUIPMENT
BACKFLOW PREVENTER, HEATER WATER FEEDER
CARBON MONOXIDE - CO
CHECK VALVES, WATER SUPPLY
CHEMICAL CONTAMINANTS in WATER
CHIMNEY INSPECTION DIAGNOSIS REPAIR
CLOGGED SUPPLY PIPING
DEBRIS in WATER SUPPLY, Water Heater
DRAIN a WATER HEATER TANK
ELECTRIC WATER HEATERS
FLOODED HEATING EQUIPMENT REPAIR
FLOODED WATER HEATER REPAIR
GALVANIC SCALE & METAL CORROSION
GAS BURNER Flame & Noise Defects
GAS FIRED WATER HEATERS
GAS PIPING, VALVES, CONTROLS
HOT WATER SUPPLY
INDIRECT FIRED WATER HEATERS
MANUALS & PARTS GUIDES - HVAC
MIXING / ANTI-SCALD VALVES
NO HEAT - NO HOT WATER: HEATER DIAGNOSIS
NOISE / SOUND DIAGNOSIS & CURE
NOISE CONTROL for HEATING SYSTEMS
NOISE, PLUMBING CHECKLIST
NOISE, WATER HEATER
ODORS GASES SMELLS, DIAGNOSIS & CURE
ODORS IN WATER
PIPING IN buildings, Clogs Leaks Types
PLASTIC Plexvent / Ultravent RECALL
PLUMBING FIXTURES, KITCHEN, BATH
RELIEF VALVE LEAKS
RELIEF VALVES - Water Heaters
SCALE REMOVAL, WATER HEATERS
SEWER GAS ODORS
SOLAR HOT WATER HEATERS
SOOT on OIL FIRED HEATING EQUIPMENT
SPILL SWITCHES - Flue Gas Detection
TANKLESS WATER HEATERS
Temperature Pressure Relief Valves - Water Heaters
THERMOSTATS, WATER HEATER
TIMERS for ELECTRIC WATER HEATERS
WATER CONSERVATION MEASURES
WATER CONTAMINANT LEVELS
WATER HAMMER NOISE DIAGNOSE & CURE
WATER ODORS, CAUSE CURE
WATER PIPES, Clogs Leaks Types
WATER PRESSURE & FLOW MEASUREMENT
WATER PRESSURE LOSS DIAGNOSIS & REPAIR
WATER QUANTITY IMPROVEMENT
WATER SOFTENERS & CONDITIONERS
WINTERIZE A BUILDING
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.
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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.
Other Water Heater Problems Caused by Hard Water & Scale Deposits
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, 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.
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.
Additional tips on draining a water heater tank can be found at ELECTRIC WATER HEATERS
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
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
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
See WATER SOFTENERS & CONDITIONERS for suggestions about dealing with hard water in buildings.
For a more broad list of noises traced to heating equipment, also see HEATING SYSTEM NOISES.
For the broad topic of controlling plumbing noises in buildings see SOUND CONTROL for PLUMBING.
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.
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Frequently Asked Questions (FAQs) about water heater noises, significance, diagnosis, repair
Question: My 8 year old water heater is making a noise
Thank you for this article. I'm hearing a noise from the water heater, that should be it. 8 years old! - Frank 8/16/11
Glad to help, Frank, let us know what you find - doubtless it will help other readers. And we welcome questions or content suggestions about articles found at InspectAPedia. Dan
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
I add that an on demand heater too can have serious trouble with clogging if the incoming water is hifgh in minerals. You would be better off installing a water softener.
Question: water was drained twice but it still makes noise
I have a Eco Water Heater that is 21/2 years. It makes a lot of noise.
Ruben, draining a water heater alone probably won't remove caked-on mineral scale deposits on the heater bottom or on its heating elements if it's an electric unit. You need to look at WATER HEATER SCALE - De-Liming Procedure.
Question: noisy attic water tank sounds like pipes banging together
My water tank in the attic is so noisy, my pipes sound like there banging together plus the toilet cistern is constantly overflowing! So frustrating. - 9/12/12
I don't think that a water heater is going to have much to do with a toilet cistern problem - more likely that's a problem with the fill control valve in the toilet. Take a look at TOILET REPAIR GUIDE.
Question: 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
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: electric hot water tank making tapping sounds like a marble being tapped on the tank interior
Have an electric 80 gallon hot water tank that services one side of my house and a 40 gallon that services a guest bathroom on the other side of the house. We have hard water which can leave hard build up in sinks and showers if not cleaned regularly. Tonight I noticed that my 80 gallon tank is making periodic tapping sounds (much like a marble being tapped on the inside of the tank). I turned the electric off but it is still making those tapping sounds. Husband says not to worry about especially since the electric is off, but it is driving me crazy. What is causing it to suddenly make these noises? - A Harris 11/20/12
Indeed Mrs. Harris, a scaled-up water heater may make a tapping sound as hot gases form on the scale-coated tank bottom and as bubbles and water are disturbed in the tank as a result. If that's what's going on it's not always an immediate safety concern, as we've seen scale-coated water heaters remain in use for even a decade without a catastrophe. But ...
Watch out: if the water tank is not de-scaled the not only will the noises worsen, but it's possible for the tank bottom to be weakened, eventually leading to or contributing to a catastrophic water tank failure, described over at BLEVE EXPLOSIONS.
Question: water leaked into the water heater insulation between the tank and outer jacket - how do I get rid of it?
I have a new electric hot water heater. When installed the cold water valve was not tight and water has dripped into the LINING BETWEEN the tank and case. The bottom is full of water. How do I drain this? - Debbie 12/11/2012
Reply: how to dry out a flooded or soaked hot water heater tank
Incidentally, when the water heater gets hot you may hear a hissing sound and see some steam coming out of seams in the water heater jacket - if so that means you are successfully drying out its insulation.
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