Question about Bosch AquaStar Indoor Natural Gas Tankless Water Heater with Vent Hood #125

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We have a 7-year-old 125B. When we turn off the hot water, the heater does not turn off. It overheats, makes a terrrible noise, water is spewed everywhere, then it turns itself off. We rebuilt the water valve and that didn't work. Any suggestions?

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Possibly the flow switch is in need of replacing

Posted on Aug 26, 2010

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1 Answer

I have a bosch aquasar 125b tankless water heater and the burners do not light when hot water is turned on this also causes the pilot light to go out


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"Infinity 20" probably 8yrs old now. Recently started making a humming noise whilst in use. The noise continues 15secs or so after hot water tap has been turned off.


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1) If tankless is not showing error code, the problem might be single-handled faucet cartridge:
http://waterheatertimer.org/Crossover.html
http://waterheatertimer.org/Troubleshoot-Bosch-Tankless-water-heater.html

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Sounds like a squirrel inside water heater


Hi,
The noise is inherent in electric hot water heaters. It is the noise that the water makes when it is being heated by electric heating elements. Mineral buildup on the elements can make it worse, so changing the elements can help...but will not totally elimenate the noise. When I install a new tank and turn it on all I have to do is listen to it to see if it is working or not...even brand new will make a sound...it is the sound of hot water... :-)

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I found the manufactures website and read this specific tech bulletin. I will be replacing or repairing my water value soon.

http://www.boschhotwater.com/Portals/7/TechBulletins/TWH-G1-25_Water_valve_rebuild_B.pdf

The bulletin said the following:
If the burners fail to go off immediately when the
water is turned off, usually due to mineralization in
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off immediately. If they do not the Aquastar will
overheat and shut down on safety depending on
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the problem there a relay stuck or thermostat bring on the pump & you can lower your high limit aquastat!! also the flow valves can bypass hot hot water risers time to put in a seperate water heater domestic coil are not energy efficient !!!! aquastat high limit set @ 180f deg low limit set @ 140f deg!!!
good luck!!! tim

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