Abstract: Electric heater is one of the important functional units of the pressurizer, and the electric heater sheath broken happened both in China and other countries. The broken is usually associated with leak. Leak will result in water penetration and electric heater will swell, thus the mechanical failure happens. It will cause the leak of the primary coolant circuit. A faulty insulation problem had been found during the hot functional test in a nuclear power project, and the leak flaw was found by test and analysis. In order to avoid the sheath broken, analysis and test have to be conducted to solve the problem. Researches show that only PT at welding is not enough, and it is risky. LT（He） is both important and RT is also needed at welding part. A new plan of none destructive test has been proposed. It will be favorable for the sealing performance of the pressurizer electric heater.