For all those with the Surface Pro 3 Core i7 model that had been experiencing heating problems: Microsoft is aware and working on a fix. Fortunately, this is only affecting a small number of Surface Pro 3 Core i7 owners.
The Surface devices restart and show a "Thermometer Gauge" icon when booting up. Microsoft is saying that this is being triggered before it should, and only happens during booting, and not while the device is running. This bug is affecting only a very small number of the i7 models, so if you haven't experienced it, it seems that you have nothing to worry about.
On the heating, Microsoft is saying that it is expected. They are pointing out that it is a i7 processor in a very slim portfolio, and the fan will run more regularly and at higher speeds than in other models, and that the device will run warmer. However, some users had reported the device getting so hot that they are uncomfortable hold it. Those should contact Microsoft Support, as the update seems to be targeting the incorrect booting only.
Here is what Microsoft had to say:
The Surface Team is aware of a very small number of Surface Pro 3 Intel® Core™ i7 devices that are temporarily restarting and incorrectly showing a "Thermometer Gauge" icon while attempting to boot up. Our investigation reveals that the system is triggering this event sooner than it should for some people, only when the device restarts, and this does not occur when the device is booted and running. We have an update that will address this that will be ready for our customers as soon as possible.
The i7 version of Surface Pro 3 is a first-of-its-kind tablet delivering i7 processing power in a thin and light package. As such, the increased power calls for the fan to spin more regularly and at higher speeds – and for the unit to run slightly warmer. If customers have any questions or concerns, they should contact Microsoft Support.