How do you fix a stuck sparge? Are there any tricks too getting a sparge running again when it slows to a trick or even stops completely?
(This is not intended to be a "how to prevent" the stuck sparge answer.)
One of the quickest solution I have used in a pinch is to blow air back up my exit tube from the mash tun. This tends to dislodge some of the spent grains collected in or on the sparge manifold (regardless of the type you are using). Then a quick stir and recirculate and often I am back in business.
The next step after blow back is to thin the mash a bit with some more hot sparge water and stir really well, focusing on getting down near the manifold. This is where having a well secured manifold comes in handy, so it doesn't dislodge from being bumped and banged.
Slowly reopening the valve and taking a little extra time for the grain bed to set up first before maximizing my flow settings helps too.
I've had a few stuck sparges and have used a blow back method and manipulating the malt fines bed. The important thing to remember is that you can recirculate heavily clouded runoff if the sparge is stuck moderately early. Just collect the first 30 to 45 seconds worth of runoff in a small stock pot, mix with clean sparge water, and send it back through the mash. Let your sparge run as normal afterwords. I've never had it stuck for a second time.
In my experience, getting some heat into the mash is the most important so depending on your process that may mean adding hot water or applying heat. Its amazing how much heat get lost during sparging.
If you have the ability to recirculate (RIMS/HERMS) run the recirculation in reverse which essentially floats the grain bed and brings hot wort back up from underneath. Let it settle for a few minutes and then very slowly start sparging again.
I just blow air into the runoff tube. Works every time.
For what it's worth, I had a gnarly stuck sparge unlike one I've had before and none of the tips here worked this time. It was a wheat beer and evidently there was not enough rice hulls. I blew into the valve for some time like an ornery child into a soda but nothing came out.
Ultimately I had to ladle everything (2.5 gallon batch) into another pot and clean out my false bottom tube which was completely blocked with wheat bits. Somehow air passed into it but liquid continued to be blocked until I physically removed the blockage.