Retina MacBook Pro fan running constantly

Have you tried an SMC reset? http://support.apple.com/kb/ht3964

Runaway applications can shorten battery runtime, affect performance, and increase heat and fan activity

Make sure your MBP is getting the proper ventilation.

According to the user manual it states in part:

"Do not operate your MacBook Pro on a pillow or other soft material, as the material can block the airflow vents. Never place anything over the keyboard when operating your MacBook Pro. Never push objects into the ventilation openings."

MacBook Pro: Care, Use, and Safety Information

"Do not place your MacBook Pro on your lap or other body surface for extended periods of time. Prolonged body contact can cause discomfort and potentially a burn."

You are still under warranty and/or have AppleCare, call them. Let them deal w/it.

Baby Boomer (USofA) wrote:

... "Do not operate your MacBook Pro on a pillow or other soft material, as the material can block the airflow vents...

The risk of blocking the air vents can't be emphasized enough. Assuming the physical configuration of the 15" (which I'm familiar with) is pretty much the same as the 13" rMBP, the air intake vents are only small slits very close to the bottom edge under the flat side of the base, and if the Mac is resting on anything other than a hard surface, those vents are almost guaranteed to be blocked.

Intel-based Macs: Using Apple Hardware Test

I've had the same issue for awhile now, and I figured out what caused it: iCloud's Documents and Data and Photos syncing are causing the Mac's CPU to overheat and run the fans--even if the computer isn't doing anything taxing. By disabling those two services, my fans instantly turned off, and the Mac has been buttery smooth since.

I'm guessing that they're constantly pinging the servers, similar to how DropBox decreases battery life. The issue is even apparent in the Yosemite Public Beta.

This one worked for me! Thanks!!!

I have the same problem but with just the left hand fan.

Genius bar had it in for 4 days and replaced the fan but it is the same with the new fan. I assume that it therefore must be a fan control software glitch? It appeared to start just after a software update as you suggest.

I've tried all of the resets and diagnostics and nothing fixes it. Hopefully an OSX update will fix this but the Genius Bar staff were clueless as to what's wrong.

So the problem appears to have gone away all by itself. Sneaky background software patch??

I was driving people nuts in meetings because of this issue. I tried shutting down one app at a time to see what was causing it. I use Flash and everyone dog piles on that as the problem for all battery issues, fans etc... Not the problem. It was iCloud and the new Microsoft Outlook.

Ah interesting. So it was maybe an update of MS Outlook that made it go away you think?