Hello, I bought a decrepit historic farmhouse and I am trying to bring it back to life. We are camping in it. It had no hot water, no kitchen, and no bathrooms. We are doing the work in phases and this weekend is the first time we are able to shower in our first brand new bathroom (yay! exciting!).

Our plumber installed a Navien NR 240-A tankless hot water heater to serve an eventual 3 bathrooms. After doing some calculations, he decided that one tankless located in the basement would be able to serve the whole house. However, it is quite a long pipe run to the first bathroom from the basement (bath: 2nd floor, other end of house) so he recommended a recirculating line, which we did.

So this weekend is the first time we got to try our first finished bathroom (yay! exciting!) and... the hot water never gets hot up there. It gets warm, but never hot. The tankless was set to 125. I increased it in 5 degree increments to 140, the "consumer" maximum. This produces extremely hot water in the kitchen adjacent to the hot water heater, but the water at the first bathroom is still not very hot.

I'd suppose since we live in a cold climate (current outdoor temp = 5 degrees F) the hot water is losing heat over the long pipe run. Clearly our plumber is aware of the long pipe run -- he suggested the recirculation because of it. But the issue isn't recirculation if the pipes can't retain the heat. I'm going to have a conversation with him on Monday but I wondered if some pros on this forum would be willing to give me advice on how I should feel about this situation.

I feel wronged. Our plumber got to design this system from scratch and do whatever he wanted. If he had said "and you'll need to insulate these pipes for an extra $XXX" we would have paid it as we trusted him. If he had said "we need a kryptonite pump" I would probably have said yes. What do I know about designing plumbing? Nothing. But now we've closed all the walls and the contractors have left and this stuff is supposed to work. Whatever conversation we have on Monday I have a feeling that I am not going to like the outcome. This system he designed should be working right now. However, I've never done a big job like this before. Is there a different perspective I should take?

Another option is to increase the hot water temperature further on the Navien. There is a "PRO" setting with a lot of warnings: "THE PRO KEY CAN ONLY BE USED BY FACTORY TRAINED INSTALLERS" that will allow me to raise the temperature further -- but this seems like a bad idea as it will only lead to burns in the kitchen. Is that right?

Thank you for any advice on these two questions. I really appreciate it. After spending so much on the plumbing I am very sad and I'm hoping for some perspective.