、。
The main valve's shut.
Literal
Main-valve, closing.
A minimal utterance. 元栓 ('main valve, shutoff valve') is the master valve for gas or water in a building. しまってる is contracted 閉まっている ('is closed, is in the closed state'). The sentence omits all particles — topic, subject marker, everything — leaving two content words and a state verb. This is extreme compression, common in quick practical speech.