Freeze Busted Tankless Water Heater Repair - DIY

Winter Storm Uri busted two of my Rinnai Tankless water heaters. I managed to fix both of them and a neighbors. I saw the same problem with a Takagi brand. !!You can do it too!! Save money and stop it from going into the landfill.
(Checkout my followup video if you prefer to do the fix with the unit in place:    • Freeze Cracked Tankless Water Heater Repai...  )

One of the most common ways that a Tankless water heater breaks is when there is a freeze and you also lose power.
Even if you remembered to turn off the water, the water inside the unit can freeze. Most Tankess water heaters have a protection against freezing. However, for that to work there needs to be power to the unit.

This is a fixable problem.
You will need to cut open the casing to get access to the crack. I used a Dremel Tool to do this. Tin snips might work but there is very little room to maneuver and there is a risk of causing more damage.

You have two options to fix this - Soldering or Brazing. Joining copper with couplings is where soldering works best. Brazing is a better solution for mending cracks. Also brazing creates stronger bonding.
Here is what you need:
1. A Fine grit sandpaper (400)
2. A copper Brazing rod - I used a Harris 5 Phos Copper Rod (A cheaper 0 or more expensive 15 will also work)
3. A Propane or Mapp Gas Torch - I used MAP-Pro Gas with a Benzomatic TS4000 torch. Any plumbers torch will work, the difference may be the time it takes to heat up the copper.

(You can buy the rod at a plumbing/welding supply place)

Get the hole as close as possible by gently nudging it back using a piece of wood. Now sand it real good and clean it well. I used some Naphta for getting it clean before brazing.You can just clean it with a wet cloth if you don't have Naphta or mineral spirits.

The entire brazing process should not take more than 3 minutes. Get the weld as thick as possible. Go at least 1/2" past on both ends of the crack.

Tips:
0. There is really no need to take the unit out to do this. I have also done this job with the unit in place by just shutting off the Electricity, Gas and Water Supply. Make sure and drain it out completely.
1. Protect the wiring in the proximity by using a piece of metal.
2. Bending the end of the rod helps you get better access.

Diagnostics:
1. On the Rinnai, if you get an error code 11 after you bring the unit back on. Check your Gas input.
2. On the Rinnai, there is a white sheathed wire on the right side that is close to where you may be doing the brazing. This has a thermal fuse inside. If you get too much heat to it, you may damage it. This will give you an error code 14 when you bring the unit back on. The short-term hack is to bypass it but I do NOT recommend it. You can find this part at many outlets online (search for "Rinnai thermal fuse").
3. If the error code 14 persists then you may have to do a "Flushing the Heat Exchanger" procedure described in the user manual

The background music by Johan Brodd called Happy Walk (https://opengameart.org/content/happy...)