Suddenly having problems after ten-twelve years of flawless performance. So I flushed the system to remove scale with vinegar, I rebuilt the water valve twice, because the burners are not shutting down when the water is off. In fact, even when you light the pilot, the burners kick on. According to the technical manuals, this all has to do with the water valve. Assuming that I rebuilt the water valve incorrectly, today I bought a new assembled valve from Bosch. But after installing it, the same thing happens. Bosch won't talk to homeowners, even though they will sell me parts. I'm extremely frustrated. The burners work, the unit heats, I just can't get the burners to shut down when no water is running through it. Sometimes the pilot won't even light unless I have water running through it. Then it starts heating the water. But as soon as I shut off the hot water, the burners keep heating until the water in the unit boils and it makes a horrible squealing sound before blowing out the pressure release valve. I tried calling a repair place but they said it's not worth repairing which I assume really means, they don't know what's wrong. I've seen several other posters here with the same issue, so I know I'm not alone. Please help!
You are looking for a mechanical problem for an electrical issue. This unit is controlled by an electronic board. That board is the cause of your issue. They are about 300 dollars.
SOURCE: Tankless water heater pilot light will not stay on
It is most likely the water valve stuck open, telling the controls to heat water, that it thinks is flowing through it, but without actual flow it overheats. Depending on how comfortable you are with taking it apart yourself, you could open the valve to see if it just needs cleaned out, or if you have a ruptured diaphragm or some other cause.
SOURCE: bosch hot water service 16p burner shuts down
a tankleess water heater doen's have a piliot? but check the vent outside make sure nothing is blocking it, if it detects the exhaust thru the cold air intake it will shut off and over heat, other then that it would have to be the control board
SOURCE: Bosch AQ125BNG Burner goes out even though the
Often, this is the result of a restriction of exhaust gases. This type of hot water heater must be adequately vented, (per installation specs). I found this out after taking a number of cold showers. :^( Two years later, and still counting, no more problems. :^)
SOURCE: I have a Bosch AquaStar AQ-125-BNG tankless water
there is a small dia copper pipe which has a thermal coupling on it the end of it sits in the flame of the pilot light,
if it fails which it does after about 25-15 months,it shuts down the gas burner
SOURCE: bosch aquastar Aq125-hx does not
That particular tankless water heater has hydro-generated ignition. In order for it to function, it requires a certain water pressure and velocity. You can try turning on the hot water in two location in your house to see if that gets it started. If it does, try getting a higher flow shower head, or removing the limiters in your faucets.
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FIXED IT. The water valve has a pushrod that moves up and down with water flow. Since I replaced the entire valve and it didn't fix the problem, I looked to see what it pushes against.
It pushes against a similar rod in the gas valve. I sprayed it with WD40 and grabbed the rod with a pair of needle nose pliers and gave it tug. It was stuck solid. After pulling a pushing a few times with the pliers, it suddenly loosened! Put it all back together and now it works!
Yes!! That did it for me too....after I had replaced the water valve and the same thing happened. The WD and moving it with needle nose did the trick. Many thanks!!!
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