Who is Liable? So many parties involved!

[Chris Bell]

This is a long story - I will try to summarize.  If I miss something, please ask.  All thoughts very appreciated!

A tankless water heater was installed before I owned the house.  I had my plumber service it and during service, damage occurred.  The damage is result of the tankless being installed improperty (the dump line was ran, and hidden away under the furnace where it was not connected to anything and not visible).

Through the serial number, my plumber found who purchased it (Plumber C).  Plumber C also filed a permit with the city (of Dallas) for inspection.  It failed inspection and was red-tagged.

My plumber said Plumber C is liable, under law, essentially because of the red-tag.  Statue of limitations has not run out yet.  I asked another plumber for an unbiased opinion on the "plumbing law" and he agreed that Plumber C, who installed it, is responsible for damages.

Plumber C's insurance apparently does not have the provision to cover this damage, I'm not sure why as I don't understand all the insurance jargon, nor do I completely trust that the insurance company is just loopholing and trying to avoid a payout (the damages were about $10k).

I don't want to put a claim in on my insurance because my deductible is (in my opinion) expensive and I don't want a claim against me (this is my personal residence). 

If I have to use MY insurance (if Plumber C insurance deny's the claim), will the subrogation process (my insurance going after someone else who's at fault) go after Plumber C's insurance?  Will they go after the previous home owner who did not disclose (on seller's disclosure) that the tank was installed incorrectly (they must have known because they were the owners during the installation)?  Or will they go after the title company (someone mentioned this to me), because the title company did not catch the outstanding red-flag permit on file with the city?  Or will they go after Plumber C personally?  I don't mean "go after" in any mean-spirited way, just lack of a better term.

Thanks, if you read that and have thoughts.  I appreciate it.