What needs to be reset after a keg change in a long draw draft system?

After a keg change in a long draw draft system, the Foam on Beer (FOB) detector often needs to be reset. FOB detectors are designed to sense when an empty keg is replaced and help prevent foam overflows that can occur during this transition. When a keg is empty and the FOB system has activated, it prevents beer from flowing until the keg is changed. Resetting the FOB ensures that the new keg is properly recognized by the system and allows for efficient beer flow without excessive foaming.

The other options, while important components of a draft system, do not typically require resetting after a keg change. The PSI regulator maintains a consistent pressure throughout the system and typically remains set regardless of keg changes. Similarly, the temperature gauge is crucial for monitoring beer temperature but does not require adjustment for each new keg. The carbonation level is also consistent if the system is properly maintained, as it's influenced by the regulator and the beer itself rather than the keg being changed.