Rad fan on + no heat from heaters

I have a 2007 X3 3.0SI that just started this problem...

After driving for 10 min or so, the rad fan will go on to it's max, while at the same time, I will have no heat coming from the heaters (however the heater fan is working). This continues until I shut the car...when I start it up again, everything is back to normal.

Temp gauge remains perfectly in the middle the whole time.

What can this be?

Sounds like it is overheating a bit - the temp. gauge apparently is designed to not move from its mid position until the overheating is serious, and then it goes in one swift movement to the red.

It has also been reported here that there is a BMW design feature that blocks coolant going through the heater when the coolant is overheating.
Theory being that you don't want to have a heater hose burst into the cabin on passengers feet.
Not absolutely sure that is factual though, but could explain your absence of heat output.

The rad fan shouldn't be on max unless there is some good reason - A/C under stress in very hot weather while idling in traffic holdup, low coolant, stuck thermostat or failed water pump.

The electric water pump in 2007+ models has been known to fail, so maybe look into that first after verifying that coolant level is correct.
Don't rely too much on the low coolant warning lamp to alert you to low coolant.

And check for any signs of a leak. But water pump may be the biggest suspect, which unfortunately can be expensive to replace, both part and labor.

Another possibility is the thermostat. I know back in the old days if they fail in the closed position, your symptoms are identical. I have heard that the electric pump does not give warning of impending failure, but you might be in luck.

Get it into the shop ASAP. If it is indeed the electric water pump, when it goes you will be stuck on the side of the road. An overheated BMW engine is a very very bad thing.

If its the thermostat, someone posted a DIY yesterday. About a $200 part and about 2 hours of labor.