Exchange Calendar sync loops, drains, and fails
I logged in to the webmail (OWA) and there Options -&gt; See All Options -&gt; Phone
Two devices were listed, my old phone and the current. I removed both. Then I restarted the phone and the sync seems to be back in order. The phone hasn't run hot for several hours and both mail and calendar events works fine.

PS. Before this I had also Reset Network Settings. I have no idea if this was part of the solution. DS.