Bosch Range Error Code ER26

ER26 on a Bosch range indicates that the Electric cooktop MTwisT control system has detected a relay supply voltage that is too high during the off state of the control. The MTwisT system is Bosch's touch-based cooktop control interface, which uses relay circuits to switch power to the individual heating zones. During the off state, the relay controlling power supply to this system should read minimal or zero voltage. When the control module detects that voltage is present and elevated beyond the acceptable threshold in this off condition, it flags ER26 as a protective fault to prevent damage to the control electronics or unintended heating behavior.

The most likely sources of this fault involve conditions upstream of the MTwisT control board. A line voltage irregularity, such as a voltage spike or sustained overvoltage from the home's electrical supply, can cause the relay supply rail to read high even when the control is in the off state. Additionally, a failing or shorted relay within the cooktop control assembly itself can allow voltage to bleed through when it should be fully open, triggering this detection. Internal wiring faults, including a short between the supply line and a control circuit trace, are also plausible contributors.

Because ER26 specifically references the supply voltage being too high rather than absent or low, the diagnostic focus should be on the incoming power quality, the relay driver components on the control board, and the integrity of the wiring harness connecting the power supply to the MTwisT module. Repair typically involves verifying the home supply voltage at the range's terminal block, inspecting the relay board or integrated control board for signs of heat damage or component failure, and in many cases replacing the cooktop control module assembly.