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Causes & cures of whistling, screaming, shrieking or whining noises heard at or in a gas-fired tankless water heater:
Two diagnostic recordings of resonant whistling or shrieking water heater sounds are given here along with an explanation of the cause and cure for this unbearable noise. Humming and other noises have been reported for some Bosch water heaters.
This article series 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.
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.
Noise Diagnosis & Repair Guide for Residential Hot Water Heaters
How to diagnose screeching or screaming water heater sounds - First step
In my OPINION Boshc makes high quality equipment of many varities including water heaters, but that has not made the company immune to an occasional screaming appliance - or customer. Here we go through steps in diagnosing the cause and cure of a loud whistle sound coming from a Bosch gas-fired tankelss water heater installed in San Miguel de Allende, Mexico.
Before fooling around with the heater itself - which can be dangerous, take a close look for a partly-closed control valve at the water heater inlet or anywhere in the building piping system.
In this first video you'll see me partly-closing first the heater's outlet valve, then the heater's inlet water valve - no no avail. The sound is not unlike blowing across the top of a Negro Modelo bottle.
This step didn't work for us but it's where you should start.
Cause of shrieking screaming or whistling 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 shrieking tankless water heater installed in San Miguel de Allende.
We recorded the noise in part to convince the technicians that it was not imagined, but happily this resonant whistling water heater was, if nothing else, reliable at making the screech whenever we turned up the heater temperature or the water flow rate.
I called our supplier in San Miguel, Don Pedro, who were wonderfully helpful. Christian referred us to their Bosch trained service technicians Daniel y Rene for technical support. Daniel and Rene had in fact come across this problem before, and it's also known to Bosch who cites in the water heater's troubleshooting table as a last item:
Resonancia - el aparato emite un sonido anormal (vibracion), giving this advice: contactcar con un tecninco especializado y capacitado.
The sound was traced to a resonant frequency air or exhaust movement interacting between combustion air intake and exhaust flue outlet gases.
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 by blocking air flow in or out of a gas fired heating appliance. Making a mistake risks fatal carbon monoxide poisoning. Consult Bosch customer service if you are having noise problems with your tankless water heater.
Other Reports of Bosch Water Heater Noises & Recommended Cures
Bosch Technical Support [USA]: Bosch Thermotechnology, Customer Service Operating Hours
Monday - Thursday, 8am - 6pm EST
Friday, 8am - 5pm EST
Tech Support Fax: 603-965-7581
Bosch Tankless & Heat Pump Water Heaters
General Inquiries: 1-866-642-3198
Technical Support: 1-800-283-3787
Website: https://www.bosch-climate.us/support-center/technical-support/ - see this page of Troubleshooting guides: https://www.bosch-climate.us/support-center/technical-support/troubleshooting/ that provides troubleshooting guides for
some but not all Bosch water heating products.
Bosch Greentherm 9000
Bosch Therm C 1210ES
Bosch Greentherm C 1050 ES
Bosch Greentherm C 950 ES
Bosch Therm 940 ES
Bosch Therm 830 ES
"Had it with Bosch 635ES (250SX) tankless water heater", reports "A loud, combustion-engine-sounding, house-shaking groan/grunt upon startup, and/or a loud whistle during operation that can be heard a block away" - retrieved 2017/04/28, original source: https://bungalowinsanity.com/2007/01/23/had-it-with-the-bosch-water-heater/ -
this author cited the gas control or valve as the noise source and noted that Bosch replaced their water heater. Bosch also had advised installing a check valve in the cold water supply line to avoid triggering the fan in the heater - probably they meant a pressure regulator - Ed. [copy on file as PDF]
Humming noise when the Bosch AquaStar 250SX tankless water heater (propane) is on. - retrieved 2017/04/28, original source: http://www.hot-water-heaters-reviews.com/my-bosch-water-heater-is-noisy.html
- Recommended repair: possible cause: is incomplete/insufficient combustion of exhaust gases that the unit senses causing intermittent hot water. Fix: contact a certified gas tech/plumber to bring both a Manometer (measures LP gas pressure at the unit) and an CO2 Analyzer to help read and adjust CO2 percentage of combustion gases, according to the tech at Bosch, 800-642-3111
Continue reading at WATER HEATER NOISE - home, 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.
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
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