Increasing temperature with wort

[Pawka]

I want to increase temperature of my mash, but do not want to spend water which is reserved for fly sparge.

Is it good (or bad) drain few liters of wort, boil it and pull back to mash?
Just the same way as with water.

 

[Sadu]

Go for it, have done this several times.
You can also remove a portion of the grain and boil that, like a decoction mash. You won't kill as many enzymes that way.

 

[porterpounder]

That's basically a very loose decoction. If you take out a lot of wort and boil it, any enzymes in solution will be destroyed, so if you boil too much of it you may experience conversion issues.