I won several cases where either home owner or a handyman did some work after the licensed contractor left and then later when something failed they tried to go after the contractor too no avail.
It all depends on what the contract states.
This is cosmetic, and has nothing to do with the actually function of the valve.
I think it was 2008, I did a did a basement conversion ( theater, bathroom, playroom, bar, yes the house was huge ). My sparky finished, my plastered finished, my painters finished.
I put all of the wallpapers on and did a walk through with the customer. All is good. A couple weeks later, I get a call that the kegerator outlet was was not working.
Went to verify with the electrician. He knew immediately. Found a loose neutral. In the sub panel.
I still remind him of that when I bring him in, lol.
Maybe in California or Canada, but, he could never claim I "own it " because I put on the wall plates.
Do you think you could win that case?
No difference.
(I just realized that specific job is how I first found this forum )