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Hello my name is ***** ***** I look forward to helping you.
I am a certified factory trained repaire tech and installer for Rinnai, Takaghi, Noritz, Navian, and Bosch. Backwards flow like that can come from any of your single handle faucets or shower valves. Are you concerned about it with your tankless?
No real need for concern. Cold water is forcing itself into the hot system because the pressures aren't equal. Once you have pressure on the hot side it'll be okay. For additional piece of mind put a spring check valve on the cold side feeding the Takaghi.
Does this answer your question?
I didn't ask for a call. My answer is there is no need for concern. If you are still worried just put a spring check valve on the cold water side. It will prevent backwards flow.
Does that makes sense? I'm willing to clarify it if you can tell me what part you need help with.
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