We're asked this question quite a bit in support. Because sliders have a starting value, customers want to know whether this value is recorded if the survey respondent does not interact with the question. The answer is no. Survey respondents must interact with the slider in order for a value to be recorded.
For example, the below slider question has a starting value of 3. When the respondent clicks on the slider bubble notice how the slider activates by changing color. If the respondent clicked Next or Submit at this point, the starting value would be recorded, however, this is ONLY recorded if the respondent clicks on the question.