thunderbolt display overheating fan running
I have a Thunderbolt display connected to a mini. Has been running well for 3 years, now the fan runs anytime the display is not in sleep mode. Installed all firmware updates, upgraded the mini OS, checked all cables. Have eliminated the mini by attaching another thunderbolt display and it runs properly. Any advise before I take it into Apple store?
Mac mini, OS X Yosemite (10.10.5)