What are the signs of a faulty oven heating element?

Please verify the following points and require itemized written supplier responses:（commercial oven oven-elements） Signs include no heat in a mode, slow recovery, cold areas, abnormal element color or visible damage, although controls or wiring may also be responsible. Disconnect power and use qualified service personnel with matching replacement parts. Define capacity, accuracy, materials and operating environment before requesting quotes on a uniform basis. Request specification sheets, test reports, certificates, maintenance manuals and spare-part lists. During acceptance, verify appearance, dimensions, functions, safety protection and packaging, and keep test records. Do not compare unit price alone; include customization, freight, spare parts, after-sales support and downtime risk. Keep written records of inquiries, confirmations, FAT, acceptance and warranty commitments.