How to "help" bring final gravity down after 2 weeks in fermentor

I brewed an all grain dry Irish stout about 2 weeks ago. I used 6lbs Maris otter, 2 lbs flaked barley, 1 pound roasted barley and about a half a pound of DME with 15 minutes left. I mashed in at 158 and let the temp drop to 152 for 1 hour, sparged and got about 5.5 gallons of wort. Boiled for 1 hour, cooled and pitched safale 04. My starting gravity was 1.040. 4 days ago I took a reading and it was only 1.020. I need it to be at about 1.008. Does anyone have any recommendations on how I can salvage this batch?  I need this for St. Patty's day!!!

It sounds like you might have mashed a little higher than 158F.  If you mash too high, you'll get a lot of unfermentables.  Since it was a Dry Irish Stout, the style guidelines suggest a Medium to medium-full body.  However, for lower gravity versions, the style guidelines allow for low- medium to medium gravity.  You probably would have had better attenuation with a mash temp from 150F to 154F. 

However, it's probably not going to be that big of a deal.  For one thing, a fuller-bodied dry stout is not the end of the world.  It would be great if you could get more out of the yeast though.  If it doesn't come down anymore, you'll end up with a fuller bodied session type sweeter dry stout.  That isn't necessarily a bad beer.  It may not win any awards at a brewing competition, but it wouldn't be because of the taste, but it would be that it was to sweet for the style.

Now, to try and help.  You have one thing going for you, which is that enough fermentation has occurred already to set the taste profile.  You can try making a starter with a much more aggressive yeast strain that will eat through anything.  I would probably end up asking for a yeast strain to use for this too.  I've had good luck with high attentuating yeasts such as London Ale yeast (Wyeast 1028).  It attenuates up to 79%.  You could also try White Labs Super High Gravity Yeast (WLP099).  It attenuates up to 85%.

Neither of these should affect flavor much at this point.  However, I would suggest that you make a healthy 1-liter starter and pitch it at high krausen.  You want the yeast to be at the correct stage of their fermentation, so that they have optimal conditions to take over and do their thing.  Make sure when you boil your starter wort to remember to put some yeast nutrient in it.  Give them the best chance you can.

Another option that you should probably try first, is to move the fermentor to a warmer place and swirl it around to get the yeast you already have in their blended.  Just make it all cloudy.  This might wake them from their slumber and get them going again.  A warmer place for the fermentor might help too.

You could try pitching the same yeast strain, but I've never had that work for me.

wow, thanks for the input. I think I'll re-pitch as you've suggested. I tried to mix the yeast around to "wake" it up but I didn't see any improvement. I'll probably go with the irish ale yeast but I'll do some research on high attenuation yeast!

can I ask how you are taking your gravity measurements? hydrometer or refractometer?

if hydrometer have you calibrated it recently (should read 1.000 in water ~ 60 degrees)

if refractometer you have to make adjustments for wort that is fermenting. beer smith has a decent tool for this as does sean terrill.

158 is a bit high but I don't think that could account for a 1.020 FG.

have you checked your thermometer for calibration?

and finally (probably should have been first) are you sure it's done? have you had a couple readings a few days apart be the same?