Water softeners use brine tanks to remove minerals from hard water. The tanks regularly need to be regenerated to remove the minerals that accumulate in the tank. The designs of water softeners can vary significantly, but most are mostly automated. In most cases, the user only has to occasionally add salt to the brine tank. The brine tank might not refill for a variety of reasons.
Waterline Not Connected
The first thing you want to check if the brine tank is not refilling is if the water softener is connected to your waterline. The entire water softener might be disconnected from your water supply, but also check to see if the brine tank is connected to the water softener. Reconnecting the water softener to the waterline should allow the brine tank to refill.
While not applicable to all water softeners, there might be a valve between the waterline and the brine tank. This valve could be a manual valve that has been closed or an automated valve that was closed by the water softener controls. If the waterline is connected, check to see if any valves or controls are blocking off the brine tank. Most people are not going to have issues with valves blocking off the brine tank, but it is a possibility.
Salt brine tanks have a floater inside similar to the one found inside a toilet. The floater is used to determine how high the water fills inside the brine tank. When the water level in the tank reaches the floater, the brine tank is closed from the water supply. If the water floater gets shoved to the bottom of the tank, it would almost immediately cause the water supply to cut off, making it impossible for the tank to refill significantly. Make sure the floater is about halfway up the brine tank, or at whatever height is suggested by the manufacturer of the water softener.
If the salt in the brine tank is packed too loosely, the salt can change into small crystals. These salt crystals eventually start to bond with one another, creating a mass of salt at the bottom of the tank. This process is referred to as mushing. The mass of salt can block off the fill line in the brine tank, preventing it from refilling. You need to clean out the brine tank completely and repack the salt properly to fix this issue. Different water softeners can use different kinds of salt and methods of packing. Make sure you use the manufacturer's suggested method when packing the fresh salt.