We have recently self installed a tankless water heater and all the plumbing except for the part of the shower line after the hot and cold come together. Now we have no hot water in shower. Is it possible that that one part of the line is the problem?

Thanks!

What do you mean the hot and cold come together. Are you saying the hot and cold are somehow tied together. This doesn't sound right. Please clarify.

I need to ask questions to find out what you are talking about, if you don't want my help, you have succeeded. Good luck.

Denellereis, I know you are new to this site but please wait to rate someone until you understand the system. You click a key that says "inaccurate" and mygirlsdad was certainly not inaccurate, he asked for more info. Luckily your low rating did not register on mygirlsdad since you are so new, please be careful in the future. OK now to the question I think I got this pictured. You kept the verticle pipe between the shower valve and the shower arm, there is no clog there or both hot/cold would be affected. The clog is likely in the hot inlet of the valve cartridge. Clog could be debris from the old tank swap out. Do you need help cleaning the inlet port of the cartridge?

Ok, I misunderstood the hot and cold coming together. I guess you meant hot and cold at the shower valve. My mistake. Most likely the problem lies at the valve itself, most likely in the cartridge as Ball suggested. Please let us know what you find, or if you would like more advice.

I agree with MygirlsDad77: it is most likely dirt inside your shower cartridge. You will have to remove it and clean it.