So I turned the heat on in my rover the other morning and after about 10 minutes it started to overheat. I turned off the heater and the temp gauge returned to normal after ab 1 minute. It has not overheated since ... What would cause it to overheat only when turning on the heat?

 

No connection between the two events.
The temp sensor could be failing, or the wiring faulty (shorting(ish) throu the heater wiring circuit).
you need a Temp multimeter with temp probe inserted between the rad fins to somewhat accurately measure the coolant temp. Then put the heating on and see if the coolant temp surges.
Yeah, weird symptoms.
Easiest test is to replace the ECT sensor (Engine Coolant Temperature)

SD