Lautering is one area where fancy equipment can't compensate for technique. Most brewers have experienced a stuck runoff at one time or another. If it happens during vorlauf (recirculation), it is relatively easy to fix: Simply stir the grain bed, allow it to settle for a few minutes, then restart the vorlauf at a slower flow rate. Scary, but not too awful. If it happens during the sparge itself, you'll have to stir the bed periodically to maintain the liquid flow, which means you'll probably end up with some cloudy wort. The resulting beer can still be quite drinkable, though. The best solution is to avoid the problem in the first place. Assuming you don't have some inherent flaw with your system's design, some fine-tuning of your technique can help.

Avoiding a Stuck Lauter
Underlet: The grain bed needs to be well established so that wort will flow at a reasonable rate and clarify it adequately. If you are using a false bottom in your lauter tun (or combi-tun), add hot water to cover the false bottom before adding the grain. This process is called underletting and will help prevent the grain bed from becoming too compacted.

Control the speed of runoff: The grain bed can also be compacted if the wort is run out too quickly during vorlauf or sparge. Be patient.

Depending on your system, you can control the flow rate using a ball valve or a pinch clamp on a piece of tubing. It should take 45-60 minutes to run the sparge water through the grain bed. Sparging more quickly will result in lower efficiency, but some home brewers would rather use extra grain than spend an hour sparging.

Get a proper crush: Milling the grain too finely is a very common cause of a stuck lauter. If there is an inadequate amount of intact husk material, the fine particles will stop liquid flow through the bed.

Control wort viscosity: High molecular weight proteins and beta-glucans increase wort viscosity and slow the lauter. Raw grains, such as unmalted wheat and oats, tend to be high in these tun-clogging substances. Using a step mash that emphasizes the appropriate temperature rests will minimize these problems.

Wort viscosity is also dependent on temperature. Higher temperatures decrease a liquid's viscosity, so a well-insulated lauter tun will promote the free flow of wort. The temperature of the grain bed should be maintained as close to 168 °F (75.5 °C) as possible. In my experience, an all-barley malt grain bed can get as low as 145 °F (63 °C) without any problems, but it is best to keep the temperature higher.

Consider your malts: Wheat and rye malts present special challenges to the brewer because they lack husks, which means they contribute nothing to the filter bed. Use of these grains makes it that much more important to have plenty of intact barley malt husks (or to use oat or rice hulls as a lautering aid).

Avoiding Cloudy Wort
Clear wort is important to the production of quality beer. Wort from the lauter tun will never be as clear as finished beer, but it should at least be devoid of large chunks. If your lauter runoff is unacceptably cloudy, the most likely source of the problem is that the recirculation volume was too small; take the time to recirculate the first runnings until they are acceptably clear. Another common cause of cloudy wort is too fine a crush during milling. Cloudy lauter runoff can also be caused by too shallow a grain bed. Modern brewers tend to use a grain bed a foot or so deep to ensure good wort clarity and a reasonable runoff time.