How to solve Java AccessControlException with LuxController heatpump (SocketPermission)

New versions of the Java JRE browser plugin seem to get even more strict and less GUI user friendly. E.g. if you try to access your LuxController 1.6 heatpump Java web interface, by default you get an exception like

AccessControlException: access denied (“java.net.SocketPermission” “x.x.x.x:8888 “connect,resolve”)

(where x.x.x.x is your local heatpump IP). This even happens if you have already added the IP to the exception list (“Configure Java” -> Security -> Exceptions).

What you can do to solve this is to edit C:\Program Files (x86)\Java\jre1.8.0_xx\lib\security\java.policy (replace “jre…” folder with your current version). Use e.g. Windows Notepad and run it with admin permissions to make the file writable.

In the “grant” area, add this line (use your heatpump IP):

Save the file and re-open your browser.