Hi,
Are you printing PLA or ABS?
I also had small warping with PLA, but only minimal. I printed directly on a glass plate.
For PLA you need a bed temperature of around 50° C. I print first few layers without fan, that it sticks good to the bed, then I had no more warping...
Be careful when using a fan on a normal glass plate. My glass broke this way, due to the different temperatures on the glass.
Now I use a special glass, temperature resistant to 800° C and no problems...
For ABS the bed should be around 100° C and you need Kapton that it sticks well to the bed.
Its just a trial and error thing. Test a few bed temperatures and switch the fan on/off to get a feeling.
Overall the heated bed added a very big value to my Ultimaker!
Regards
Tristan