The amount on your W-2 with a code of "W" in box 12 is the sum of your employer's contributions plus your contributions through a salary reduction/payroll deduction plan. It is counter-intuitive, but these are both called collectively the "employer contribution" by the IRS.
Your employer's contribution and your contribution through payroll deduction should be reported only with code W in box 12, not in box 14. And since you say that your employer didn't contribute anything, then the amount in box 12 with code W must be only your contribution, and nothing should be represented in box 14.
Because of the understandable confusion on what "employer contributions" refers to, it happens that taxpayers often enter their own contributions a second time in the HSA interview.
On the screen entitled "Let's enter [name] HSA contributions" (see screenshot below), it's tempting to enter "your" contributions from the payroll deduction on the second line ("Any contributions you personally made").
However, your contributions that are in box 12 are already included in the first line ("2016 employer and payroll contributions"). In this case, you would enter zero on the second line (unless you actually made some contributions to your HSA outside of your employer).
The common result of entering your contributions twice is that TurboTax reports that you have an excess contribution for the year.
Go back to the HSA interview and correct that screen.
[Edited 3/23/2020 1:31pm CDT - corrected terminology]
