Query Builder for Result Source not working in Central Admin/ Web Application
First make sure that the SaerchWebParts feature is enabled.
Enable-SPFeatureSearchWebParts-url http://<Web application URL>
Second make sure the connection to Search Service is made
Central Admin | Manage Web Applications | Select Web Application | Select Service connection in action bar | check Search Service Application
Third make sure that the crawler is running, give it some time for crawler to run and index the result and after some time the result should be shown in search results.