Washed yeast and high FG

The last few AG batches I've made with a washed S-04 have ended with rather high FG. Could I be underpitching? I use one half pint jar of washed yeast.

How long did you store the yeast or was it a wash/pitch deal? If stored it any length of time, I've found that a starter is indispensable.

I'd say it was stored for less than a month, maybe two.

That'll do it. Did you make a starter or just pitch? The washing process is hard on the yeast....the storage really hurts. You may have lost 50% or more of the viable yeast when you stored in the fridge (I'm assuming you used the method in the 'yeast washing' thread.) Hence the need for a starter. Some people get away with just pitching from their mason jar, but my results have been sub-par (at best) when I did that. By making a starter your really giving the yeast the head start in reproduction they need.

You need to make a starter, esp with washed yeast.

Yep, made a starter every time I used my washed yeast. Could I be underpitching? How about temps? I've been trying to keep them at around 70 degrees.

Well, underpitching will have to be determined by your OG. http://www.mrmalty.com/calc/calc.html seems to be the standard. In my own brewing process (read learning curve), I've found high FG for me usually meant I missed my mashing temps. Until I got a digital thermometer that I could calibrate....it was just a guessing game. Comparing my 'good' thermometer with the others I've found the range of failure was anywhere from 3 to 9 degrees! For checking meat on the grill that'll work just fine....for beer...really screwed up a couple of brews for me!!!!