Got to agree with the above. Definitely something wrong. Most of the heat comes from the base - or it should. On full setting the heat is very noticeable, half setting is quite mild.
If you can't really tell on full after 10 minutes then it's definitely broken. The slight warmth you noticed will probably have been you warming the seat - body temp being above 30 degrees.
Try connections like Mike says, then the fuse, otherwise you've got a bill coming your way. Can't belive you hardly use them, mine are permanently on during the colder months, just switched to half already. Mind you I've got a roadster and it's \ bit chilly with just a frozen bit of canvas covering the car in winter !