(T) Overheating and cold/hot heating

I own a 2004 Punto 1.2 16V, only 22k kms on the clock.
From few days ago, I have a problem with overheating, but only when driving very slowly or standing. When I drive normally, temp gauge is rock solid where it should be. Also, as today was first winter day, and I bought the car in spring, I noticed that heating seems to work very strange. It took very long to un-freeze the windshield, and heater blows hot air for a while, and after that cold. I didn't move the switches.
No power loss during driving, engine works like a charm.
Any ideas?

you need to bleed your radiator there is air in it. Alot probably