Your reply from THOR is interesting. Everything I have read about the tankless is that it is winterized through the regular plumbing. The reason there is a bypass vale in the heater with a tank is so that you don't fill the water heater tank with 6 gallos of antifreeze.
Since there is no tank with the Girard Tankless water heater, I can't imagine what a bypass valve would accomplish.
Here is a link to the Girard Tankless Water Heater.
https://www.manualslib.com/manual/76...tml#manualRead the section on winterizing. You'll see no mention of a bypass.
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