Check for updates doesn't work?

When clicking the “Check for updates” option inside any Spark client on our network, I always get a response that there are none available… even though the latest version is 2.5.8 and some of our machines have 2.5.6 or 2.5.7 still installed. Is this button checking somewhere on our server for updates or is it attempting to pull from the IgniteRealtime servers?

That depends on the configuration of your server and the plugins you run on it. You can install a plugin that controls the version of spark that is available to download from your own server. I purposfully have placed an older version there as users cannot install updates anyway.