If you added coolant, you need to bleed your cooling system. Air trapped in the cooling system will result in no or intermittent heat through one or more of your vents inside the car. It's probable that you're down more than 1/4 liter, but you need to bleed the air out.

__________________
2007 BMW X5 4.8i - Sport Package, Wife's Car

2001 BMW 325i - My Car.

2005 Ford Excursion Limited 4x4, 6.0 Powerstroke Diesel. My first "grown up" car.