Partial Mash isn't getting sweet

Hey guys,
I am following Deathbrewer's Partial stove top mash.
I have 2 KG of Munich in a grain bag, I have got the heat up to 160 dF twice. The first time I took the pot off the stove and wrapped it in layers to insulate. The second time I left it on the stove and checked that the temp was still around 150.
This is only my 2nd partial mash. The first one I did was with Pilsner Malt. I left the pot on the stove over night and the next morning it was as sweet as honey.
My Munich mash is only slightly sweet. It may have a little bit of the creamed corn DMS taste to it.
any ideas?

You should get every bit of the sugars out within an hour.
Temperature control is huge. You've got to have a way to keep the temp steady.

How well the grain is milled will make a big difference in how much sugars you can get out. The other (related) factor is how well you got the grain and water mixed. If you put the grains into a muslin bag and dunked them into the water, it takes a long time for the grains to get wet to the middle. Dry grains don't get the starches converted.