I maintain a rental home in California and I own my home in the United Kingdom where I've lived since 2017. What is the "location of my tax home?"

[surgerygalore]

hello!
tax home is the city or general vicinity where your primary place of business or work is located, regardless of the location of your residence, and has an effect mainly on your tax deductions for business travel.

[LeonardS]

Since you do not "work" at your rental home in California then your tax home is not California.  

Your rental home income is passive income, not income received from active employment.

Based on your question it would appear that where you live in the United Kingdom is your tax home.

This TurboTax link What is a Tax Home? has information that you may find useful.