Thermador Cooktop Error Code C8

C8 on a Thermador cooktop indicates that the internal communication bus between the main board (MB) and the auxiliary display board (ADB) is not functioning. This can be caused by a defective circuit between the two boards, an incorrect board configuration, or one or both boards not receiving power. The cooktop will not operate normally until this fault is resolved.

A power cycle or reset will not permanently clear C8 if the underlying cause is still present. If the wiring is damaged, a board is misconfigured, or power is not reaching one of the control boards, the fault will return immediately or shortly after restart. The root cause must be diagnosed and corrected for the error to clear.

Repair costs vary depending on the root cause. If the issue is a loose connector or wiring repair, labor costs may be in the range of $100 to $200. If one or both control boards need to be replaced, total costs including parts and labor can range from $300 to $700 or more, depending on the specific boards required and local service rates.

A basic visual inspection of wiring and connectors is something a knowledgeable DIYer can attempt after disconnecting power to the unit. However, if the fault involves board-level diagnostics, power supply testing, or board replacement, a qualified appliance technician is recommended. Incorrect board installation can actually cause or worsen a C8 fault, so component replacement should be done carefully.

No, you should not attempt to use the cooktop while a C8 fault is active. The error indicates that the control boards cannot communicate, which means the cooktop cannot manage its own operation reliably. Discontinue use and have the unit inspected before operating it again.