There is no requirement to have a bypass for the tankless water heater. You will need to shut the 12volt power off for it. If you take the outside door off, there is an on and off switch for it. If you don't power it off it will go to the winterize mode which will cycle it on and off.
Now back to the bypass for the water heater. Although there is no requirement for it, Thor actually plumbed one on mine. Why? Here is a link for the manuals.
https://greenrvproducts.com/pages/owner
Thor Forums
