Coupler for use in liquid heater and liquid heater

A coupler for use in a liquid heater, comprising a male connector and a female socket connector coupled with the male connector, wherein

• the male connector comprises a connecting wall and an annular cylindrical wall formed around the connecting wall, and
• the female socket connector comprises an end wall combined with the connecting wall of the male connector and a peripheral wall formed around the end wall and arranged perpendicularly to the end wall, wherein a surface of the end wall combined with the connecting wall is lowered from a center towards a periphery and is convex shaped, and the peripheral wall comprises arced sections and gapped sections connected between two arced sections, so that when the male connector is coupled with the female socket connector, the arced sections are allowed to be coupled with the annular cylindrical wall and the gapped sections do not contact with the annular cylindrical wall, and wherein the female socket connector and the male connector come into contact with each other when the female and male connectors are coupled.