Liquid heaters are usually composed of a single or multiple heating tubes that can be assembled into a detachable heating tube by TIG welding or silver brazing on a fastener (thread, flange, etc.) according to design and usage requirements. In order to facilitate temperature control, overheating protection, and extend the service life of the heating tube, the temperature control element can be placed in the hollow temperature measurement hole of the flange heating tube, and then connected to the control system.