Tankless Water Heater Failure

[Junkman]

Today, I got the tankless water heater out of the garage, but the fellow who took it off the wall didn't fully drain it, and the copper exchanger froze and cracked. I looked for a replacement part, only to find it was out of stock everywhere I looked. This leaves me with having to buy another. I was reading the installation manual (38 Pages), and it appears that it isn't as easy as just hanging it on the wall and plumbing the water lines. They mention testing gas pressures and a bunch of other things that need to be done upon start-up. Is this something that can be ignored, or is it the type of thing that I should leave for a licensed plumber? I can solder pipe and hook up gas connections, but I'm not familiar with pressure testing. I know that there are a number of professional plumbers on these forums, so I am asking for your opinion before I buy a heater and get ahead of myself in an area where I might not belong. This is an LP installation.
Also, are there brands I should avoid? The original is a Noritz, a brand sold by SupplyHouse.com

 

[carlaisle]

Assuming it was installed correctly to start, you can ignore all of that as long as the replacement is basically the same size/efficiency. If it was running correctly when removed from service, you can generally assume the installation was at least adequate. The question at this point is why was it removed from service?

 

[Junkman]

The original one was correctly installed and then removed for the renovation. My question is about installing a new replacement heater. I am not going to buy a used one since I would have no idea whether it works properly. I could wait till the service part is back in stock and R&R the damaged part. The replacement part is approximately $400, and a new unit is $1500.