I did my first all grain batch last night and went way over the desired 150s range on the temperature of my mash. It ended up being around 170f.
What effects will there be from mashing at 170 (or higher)?
If in theory all the enzyme for starch to sugar conversion were denatured, you'd have a large pot of solublized starch on you hands. There was likely some conversion however, but its hard to tell.
The biggest concern with too much non-converted starch is contamination. Brewing yeast won't go after the starch very efficiently. However, most wild yeasts and certainly bacteria will be able to use that as a food source.
Despite having used sanitizer things are not sterile and a contaminate could take hold.
This screw up will be an interesting experiment.
At temperatures this high, you will likely end up with a very sweet beer. You went high enough to halt much of the enzymatic activity that converts the complex starches into the simple(ish) maltose that the yeast like to munch on. You'll still get some fermentation, just expect this beer to be pretty sweet, cloying even. It should be drinkable, but it won't be great. I'd call it a learning experience and move on to my next batch. Don't dump it, though. See it through.
You can read more in How to Brew. Note that the online version is the outdated first edition and Palmer has now changed his mind on some of the stuff in there. I recommend picking up a copy of the third edition.
It really depends on how long you were at that high a temp. If it was for the entire mash, you likely have a pretty unfermentable wort. But it takes 20 min. or more to denature enzymes, so it may not be too bad.
I had an out of control mash. Beer came out just fine. Didn't have quite as much body as that recipe normally does. Target mash was 152, and ended up in 170s.
If you temp is too high put stir up the mash with frozen containers of water. You can bring temp down without adding any water directly to mash.
Water temperature over 170 can extract tannins from the grain, giving it off flavors. If you temp is high, remove the heat source and let it cool. Letting your mash sit for awhile until it cools to 150 will give you the conversion you need. The frozen water containers idea is great remedy for hot mash. Brewdog333