Low heat output is usually either more coolant or the thermostat is stuck open.

Get a good scanner that will read the state of the heater valves and the heater core temps real-time.

Also easier; enable the hidden menu and display real-time coolant temp. It should get to 90°C or so quickly and stay there even if ambient is 0-10°C.

The nearly useless indicator on the dashboard stays pointed straight up for about a 40°C (70°F) range of temp including temps too cold to keep the car in closed loop performance.

If you ever noticed the needle not pointing striaght up after the car's been running more than five minutes, than it's the thermostat that is defective.

When heat isn't working, first make sure coolant is topped off, then determine the coolant temp, then determine if the aux coolant pump is working. All those things are more likely than the coolant control valve.

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2011 E70 • N55 (me)
2012 E70 • N63 (wife)