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?

possible faulty pressure switch connected to the water line and that is failing to turn on the main gas tap solenoid
best have it checked by an accredited gas fitter or service center for the make

Sounds like the diaphram in the gas control valve which is not replacable. You would have to replace the gas control valve and I would also suggest replacing the thermocouple. However since the heater is 8 years old you may think about replacing the entire hot water heater. Depending on how much water has gone through it in these past 8 years it will probably rust out soon and then you will be dealing with a flood.

Good luck,

Marty

Sounds like the watervalve was never serviced. It will stick if its not serviced every 3-5 years according to the manual. If it sticks, it can keep your burners on after waterflow, and overheat the water still in the exchanger. This can cause plastic/pvc/pex to swell and burst. Thats why any machine says to have only metal lines connected for min of 3 feet.
Since it got wet, you may have to replace your control box as well, but at least maintain your watervalve and recalibrate your microswitch. Those last 2 may be your only issues.

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

2) Catch up on maintenance, such as cleaning combustion parts, have gas pressure checked, etc.

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

Sounds like an old water heater, full of rust at bottom. maybe coming to end of its life. Think new if over 7 years old. Did you replace anode rod? Probably shot also. Good Luck...

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... :-)

heatman101

If this is not a sealed combustion unit, service the water valve OR rebuild the water valve if it is over 5 years old.

Does it happen to any other fixture? If not, it's most likely your shower valve and not heater.

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
the water valve on older heaters. To test for this
possiblilty, run hot water at a faucet, then shut off
the cold inlet supply and observe if the burners go
off immediately. If they do not the Aquastar will
overheat and shut down on safety depending on
the delay.

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