It takes a few minutes for my tankless water heater to warm up, so we end up wasting a lot of water in our shower. Is there a way to avoid this? A friend mentioned a “comfort valve” or something? What is it and how does it work? Or is there another solution? Thx!
Living in the US I’ve never seen what you’re describing
What part? Most houses I’ve seen in the Northeast either have some kind of access panel, or the shower is backed by a closet in another room where you could cut in if you needed to.