Unknown valve in my 2015

[Caffeinated]

As I was winterizing my 15 27ft FC FB, I noticed something I hadn't noticed before. The hot water tank is under the bathroom sink and has a bypass valve. Underneath that, there is a white pex line, with a black plastic on off valve in the line. It was turned to the off position, and had apparently been that way for the last year and a half. Everything works. So what is it for?

Mike

[overlander63]

Some models have that as a bypass for the entire water heater plumbing. It never made a lot of sense to me, and I never got a straight answer about why it was there, though it may be something to do with some Canadian standard.