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Rick, HVAC Supervisor
Category: HVAC
Satisfied Customers: 21365
Experience:  40+ yrs. experience as a licensed oil & gas technician.
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I have an Aquastar 125-X tankless hot water heater. It has

Customer Question

I have an Aquastar 125-X tankless hot water heater. It has 2 problems that I am guessing are related. First, the burners don't ignite every time i turn on the hot water. In fact they almost never ignite twice in a row. The pilot always comes on, but more often than not that is all that happens. Second, when the burners do ignite, they usually only stay on for about 5 minutes. I've had 3 technicians try unsuccessfully to fix it. Others won't even try. Most suggest I replace it (it's at least 12 years old). I just want someone to tell me what is actually wrong and what it would take to fix it before I take that route. Please help.
Submitted: 2 years ago.
Category: HVAC
Expert:  Rick replied 2 years ago.
Was the water rebuilt? What you describe sounds like a problem with the water valve. This device is what senses water flow and modulates the burner fire.
Expert:  Rick replied 2 years ago.
Sorry for the typo. The first sentence should be > was the water VALVE rebuilt?
Expert:  Rick replied 2 years ago.
Your question just popped up again with no response from you. Did you have more questions?
Customer: replied 2 years ago.
As far as I know the water valve has not been rebuilt
Expert:  Rick replied 2 years ago.
Then that's the most likely culprit based on your description. It's a fairly common repair/maintenance item for these units. A tech familiar with Bosch should be able to handle the fix.
Customer: replied 2 years ago.
Just wondering.... What does the water valve have to do with the gas flow which seems to been the issue to me. The water is flowing through the unit fine. It just isn't being heated since the burners aren't igniting.
Expert:  Rick replied 2 years ago.
Like I said before, the water valve is what senses the water flow rate through the heater and adjusts burn rate accordingly. The water valve is an internal part in this unit it's not the manual shut off on the water line
Customer: replied 2 years ago.
What tells the pilot light to turn on?
Expert:  Rick replied 2 years ago.
The micro flow switch
Expert:  Rick replied 2 years ago.
Separate part from the water valve