In my search filter (hidden link) I have a checkbox with the number of stars. This now only shows a single value and not multiple values if, for example, 2 and 3 stars are checked.
For example:
2 stars checked: result 42775
3 stars checked: result 37368
2 and 3 stars checked: Are not shown result together.
A checkboxes filter normally works with an "OR" comparison, so if visitors check both '2' and '3' then it would show any posts that had either '2' or '3' checked.
When I just checked your site I found that checking '2' alone gave 42936 results, checking '3' alone gave 37529 results, and checking both '2' and '3' gave 42936 results, i.e. the same as checking '2' alone.
That suggests to me that all of the posts which are checked '3' also have '2' checked.
(If this is a checkboxes custom field multiple values can be checked at the same time. If that shouldn't happen and only one option should be checked at a time, you may want to use a radio custom field instead, where you can have multiple options, but only one may be checked at a time. You can still show the filter in a View as checkboxes, so multiple options can be checked when filtering, but the posts themselves would only be able to have a single value.)
All my houses only have one rating (see print screen) but I will adjust the filter to a dropdown with a minimum rating.
But now the dropdown has the value '0' but I don't have houses with the value '0'.
Is '0' shown if there is no rating?
And is it possible to not show '0' in the dropdown?
If I understand correctly, you're now using a 'select' type custom field for the ratings value.
It should only show the options/values which you've set in the field settings in the relevant field group.
If some of the posts are showing '0' as the value, when the field itself doesn't have this option, then it is possible that this value was saved from old settings of this custom field.
You can update/re-save those existing posts, so that the custom field value for this field is updated as per the new settings.
I hope this helps and please let me know if you need further assistance.