The indicator light is on, indicating that the power supply has been added to the indicator circuit. The fault lies in the electric heating tube or its connecting part. The common electric heating tube is damaged and the contact is poor. You can tell by removing the electric heating tube and measuring its resistance. The electric heating tube is damaged and can only be replaced generally. Poor contact is mainly due to the serious corrosion or deformation of the contact reed in the power plug assembly, so the switch box can be disassembled for cleaning and maintenance.