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I have an Aquastar 125-X tankless hot water heater. It has…

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I have an Aquastar 125-X...
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: 3 years ago.Category: HVAC
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Answered in 3 minutes by:
6/28/2015
HVAC Technician: Rick, HVAC Supervisor replied 3 years ago
Rick
Rick, HVAC Supervisor
Category: HVAC
Satisfied Customers: 24,582
Experience: 40+ yrs. experience as a licensed oil & gas technician.
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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.
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HVAC Technician: Rick, HVAC Supervisor replied 3 years ago
Sorry for the typo. The first sentence should be > was the water VALVE rebuilt?
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HVAC Technician: Rick, HVAC Supervisor replied 3 years ago
Your question just popped up again with no response from you. Did you have more questions?
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Customer reply replied 3 years ago
As far as I know the water valve has not been rebuilt
HVAC Technician: Rick, HVAC Supervisor replied 3 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.
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Customer reply replied 3 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.
HVAC Technician: Rick, HVAC Supervisor replied 3 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
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Customer reply replied 3 years ago
What tells the pilot light to turn on?
HVAC Technician: Rick, HVAC Supervisor replied 3 years ago
The micro flow switch
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HVAC Technician: Rick, HVAC Supervisor replied 3 years ago
Separate part from the water valve
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