I suspect that you are using very thin bottomed pans. Try using an even lower heat setting and bring the contents of the pan up to the boil slightly slower. Imagine using a frying pan. If you put an egg in to fry and the pan was to hot it would burn on the bottom but be uncooked on top, At a lower temperature the egg would cooker slower but be cooked all the way through without the burnt bottom.
A trick I use went heating milk is to rinse the inside of the pan with cold water before adding the milk, Oh and again not using to high a setting this way I rarely get any burnt areas.
If you can face the outlay a pan with a built up base will distribute the heat evenly and at least the way the burnt bits will be evenly spread.
