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Error code reference

Bosch Range Error Code ER12

Electric cooktop MTwisT control mismatch of relay port pin and software register.

Bosch codesBosch range codes

Electric cooktop MTwisT control mismatch of relay port pin and software register.

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What ER12 means on a Bosch range

ER12 on a Bosch range with an Electric cooktop MTwisT control system indicates a mismatch between the physical relay port pin state and the corresponding software register value. The MTwisT control system uses a microcontroller to manage the switching relays that supply power to each induction or electric cooking zone. The software continuously monitors register values that are supposed to mirror the actual hardware state of each relay port pin. When the firmware detects a discrepancy, meaning the physical pin output does not match what the software register expects, ER12 is triggered to prevent uncontrolled heating or unsafe relay behavior.

This type of fault typically points to a failure within the cooktop control board itself. The relay driver circuitry, onboard firmware, or the relay hardware may have developed a fault that causes the pin state to diverge from the register value. It can also result from a corrupted software state caused by a power surge or brief voltage anomaly, which may scramble the register values without changing the actual hardware output. In some cases, loose or corroded wiring connections between the control board and the relay assembly can introduce signal inconsistencies that the controller interprets as a mismatch.

Because the fault is tied to internal register and hardware synchronization, external component failures such as a burned cooking element are less likely causes. The diagnostic focus should be on the MTwisT control board, its relay outputs, and the integrity of the associated wiring harness.

Source: manufacturer service documentation.

Common causes of ER12

  1. 01

    Faulty MTwisT control board

    Part replacement

    An internal failure on the cooktop control board, such as a damaged relay driver circuit or corrupted firmware state, is the most likely cause of a relay pin versus register mismatch. Inspect the board for signs of burning, failed solder joints, or damaged relay components.

  2. 02

    Power surge or voltage anomaly

    Wiring / connection

    A sudden power surge or voltage spike can corrupt the software register values on the control board without physically changing relay states, triggering the mismatch error. A power cycle may temporarily clear the fault if this is the cause.

  3. 03

    Loose or corroded wiring connections

    Wiring / connection

    Poor connections between the control board and the relay assembly can cause intermittent signal discrepancies that the controller reads as a pin-to-register mismatch. Check all harness connectors at the control board for corrosion, looseness, or damaged pins.

  4. 04

    Failed relay on the control board

    Part replacement

    A relay that has mechanically or electrically failed may hold a state that the software register does not expect, producing a persistent ER12 fault. This typically requires control board replacement since the relays are often integrated into the board assembly.

  5. 05

    Software or firmware error

    Wiring / connection

    In rare cases, a firmware bug or corrupted program memory can cause the register values to be written incorrectly, creating a false mismatch with the actual hardware pin states. A factory reset or firmware update, if available, may address this.

See the test procedure for each cause

Frequently asked questions about ER12

What does ER12 mean on a Bosch range?
ER12 indicates a mismatch between a relay port pin state and its corresponding software register value in the Electric cooktop MTwisT control system. The control board continuously compares the physical state of each relay output against what the firmware expects, and ER12 is displayed when those two values do not agree. This is a safety fault designed to prevent uncontrolled or unexpected burner operation. Resolving it typically requires diagnosing or replacing the cooktop control board.
Can I fix ER12 on my Bosch range myself?
Some instances of ER12 caused by a temporary power anomaly can be cleared by performing a power cycle, which involves turning off the range at the circuit breaker for several minutes and then restoring power. If the error returns immediately or persists, the repair likely involves inspecting wiring harness connections or replacing the MTwisT control board, which is a task best suited for a qualified appliance technician due to the complexity of the control system.
Is it safe to use my Bosch range while ER12 is displayed?
No, you should not attempt to use the cooktop while ER12 is active. The error indicates a hardware-to-software synchronization failure in the relay control system, which means the range cannot reliably control burner power levels. Continued use under this condition could pose a risk of uncontrolled heating. Disconnect power to the range and contact a technician before resuming use.
Will resetting the Bosch range clear the ER12 error?
A power reset by switching off the circuit breaker for several minutes may clear ER12 if the fault was caused by a transient voltage event or a temporary software state corruption. However, if the underlying cause is a physically failed relay, a damaged control board, or a persistent wiring issue, the error will return after the reset. A reset is a reasonable first step but should not be relied upon as a permanent fix.
How much does it cost to repair a Bosch range with an ER12 error?
Repair costs depend on the root cause. If only a wiring connection needs to be corrected, labor costs may be in the range of $100 to $200. If the MTwisT control board requires replacement, parts alone can range from $150 to $400 or more depending on the specific model, with additional labor costs on top of that. Getting a diagnostic assessment from a certified technician before authorizing repairs is recommended to avoid unnecessary part replacement.

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