How to avoid a stuck mash and dry-firing the heating element
Water heating elements should always be completely immersed in water to ensure that heat is quickly dissipated. If not, the element could overheat and be damaged or melt or at the least, sugars will likely scorch on the exposed element ruining your beer with a burnt/ash flavor. Many brewers have brewed hundreds of batches of beer without a single heater failure, but if it does occur, ruining a heating element by dry-firing is not a fun experience, not to mention it could ruin the batch. When they fail, elements sometimes have complete external failure (like the photo on the right) or just fail internally as is often evidence by a heat discoloration on the element (like in the photo below). Having a backup replacement element will come in handy if your element ever fails, but here are a few suggestions on how to help avoid failure in the first place.During Mash
In the BIAC, wort from the Mash Colander drains into the fermenter, and the pump pulls this wort out the bottom of the fermenter and returns it above the grain in the Mash Colander. This is useful for vorlauf and for regulating mash temperature because the wort can be heated as it exits the Mash Colander, passes the heating element, and is returned to the top of the grain bed. It is possible, however, if the pump is operating too fast, to get ahead of the flow rate through the grain, and pump all the wort out of the area under the Mash Colander where the heating element is situated. This could remove all the water from around the element and if the element is turned on at that point, it could lead to 'dry firing' of the element and burn out. This is especially true in the early stages of the mash before the grain bed fully fluidizes or if the grain crush is particularly fine, preventing good flow through the grain bed. There are a few things that can be done to avoid this.
First, increase the crush size for your grain. If you can adjust your roller width (or have your brew shop do it for you) a general width guideline is 0.04-0.045 inches. If you still have a problem, go slightly wider. If you are experimenting with gelatinous or gummy cereals (e.g. oats or rye) you can include rice hulls to help counter-act the 'glue' effect'. When using toasted or dark malts, add them after the pale malts to keep them near the top of the grain bed, as they tend to fragment more when crushing and will be more gummy. Do not add the grain too fast (which then requires more mechanical agitation), and do not overmix the grain when mashing in (mix just enough to remove air pockets). Do not move the mixer near the false bottom on the Colander as this can force grain into the bottom (perforations or wedge wire) and plug it up.
Second, if doing a single-step mash, it is not absolutely necessary to pump the wort during mash. With the Mash Colander inserted in the fermenter it is effectively surrounded by a water bath. The element keeps the water bath at the target temp for mashing, and warms the colander which warms the mash. When mashing is complete, the pump can be operated to move the water under the colander to the top of the grain bed for vorlauf. In the short period during vorlauf it is unlikely that your mash will stick or that you will run out of water in the cone portion of the fermenter where the element is, especially if the next step is followed.
Third, if circulating during the mash, or during vorlauf, if the water level starts to rise in the Colander, it means wort is being pumped out of the bottom faster than it is being replenished and it should be slowed; in time, the element will be exposed and could be damaged. To prevent the pump from moving wort to quickly, install a valve on the downstream side of the pump (either on the pump outlet or on the Mash Colander port) and partially close it to slow the amount of wort moved out of the bottom. (Don't close a valve before the pump as this 'starves' the pump and can damage it.) If grain that has fallen through the Colander plugs the pump line, attach the pump intake line to the cone side-racking port, rather than the bottom port of the fermenter.
Fourth, with the Power Controller, power output can be set to around 30% during mash which is more than enough to maintain mash temperature, while minimizing the chance that the element will be ruined if temporarily exposed.
Incidentally, throttling the pump is also the best way to prevent pump cavitation. Cavitation occurs when the pump is pushing liquid out faster than it can draw it in. This creates a vacuum which causes a 'cavity' to form, which prevents efficient operating of the pump. When the flow is throttled back on the exit side, it prevents liquid from being pushed out faster than it can be drawn in, preventing the cavity from forming.
To ensure that the water level will not drop to the point where the element is exposed, you need to first observe/calculate the volume during filling at which the element is fully covered. Then add 10-20% volume as a safety buffer and have this as your minimum water/wort level in the vessel. Then check all your recipes and ensure that at no point during heating will the volume level ever be below this. And it is always best practice to never be too far from your equipment on brew day. There have been reports of customers leaving during the boil to run a few errands and returning to find their element dry-fired and is ruined.
The same rules apply during fermentation as during mash and boil—keep the element covered with water at all times. When using the element to keep the beer warm during fermentation, it is important to keep the power output on the Power Box set to less than 3% to ensure that yeast that sticks to the element does not scorch. This will also likely prevent dry-firing the element as at such low power output, the heat can dissipate, however, it is still best practice to always ensure the element is fully covered.