Enterprise Gateway to on-premise AS cube timeout?

With the latest version of the PowerBI Enterprise Gateway installed on a server (that's never switched off) and a live Data Source connecting to an on-premise Analysis Services multidimensional cube (SQL 2012) we successfully deploy a report and dashboard, and successfully test refreshing and interrogating. The databoard works via the PowerBI website and apps, no problems.

After a period of non-use, we try the report again and find that it's no longer able to refresh and the Enterprise Gateway is said to be down, with the host unreachable.

Is there a timeout somewhere after a period of inactivity?

I thought that I might create a non-live Dataset and schedule this to periodically refresh, but then find that scheduled data refreshes only use the Personal Gateway, not the Enterprise Gateway, and so presumably this isn't going to be of any use.

Any ideas why the Enterprise Gateway stops working after a while?

Thanks