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Error code reference

Bosch Cooktop Error Code ER 25

False connection of mains supply detected.

Bosch codesBosch cooktop codes

False connection of mains supply detected.

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What ER 25 means on a Bosch cooktop

ER 25 on a Bosch cooktop indicates that the control system has detected a false or incorrect mains supply connection. This means the cooktop's internal monitoring circuitry has identified a wiring configuration at the power supply input that does not match the expected electrical setup for the unit. The cooktop continuously monitors its incoming power to verify proper phase configuration, voltage levels, and neutral or ground connections. When the detected supply does not align with the unit's requirements, ER 25 is triggered as a protective measure to prevent damage to internal components or a potential safety hazard.

The most common root cause involves incorrect installation wiring at the terminal block where the cooktop connects to the household electrical supply. This can include reversed line and neutral conductors, incorrect phase connections on three-phase models, or a missing neutral wire. On induction and electric cooktops, the mains input is also monitored for voltage balance across multiple legs, so an open or improperly terminated conductor can produce this error even if the unit appears to have power.

Because this code points directly to the incoming power supply configuration rather than a failed internal component, the diagnostic focus should be on the wiring at the junction box, the terminal block connections inside the cooktop, and the supply voltage at each terminal relative to neutral or ground. A qualified electrician or appliance technician should verify correct supply wiring before any internal components are inspected or replaced.

Source: manufacturer service documentation.

Common causes of ER 25

  1. 01

    Incorrect wiring at the terminal block

    Wiring / connection

    The most frequent cause is improper connection of the supply conductors at the cooktop's terminal block during installation or reinstallation. Reversed line and neutral wires, or conductors connected to the wrong terminals, will immediately trigger ER 25.

  2. 02

    Missing or open neutral conductor

    Wiring / connection

    If the neutral wire is not connected, is loose, or has broken continuity at any point between the breaker panel and the cooktop terminal block, the control board will detect an unbalanced or incorrect supply and generate this error.

  3. 03

    Incorrect phase configuration on multi-phase supply

    Wiring / connection

    On cooktops designed for three-phase or split-phase supply, connecting phase conductors to the wrong terminals or using a single-phase supply where multi-phase is required will cause ER 25. Verify that the supply voltage and phase configuration match the cooktop's rating plate specifications.

  4. 04

    Loose or corroded terminal block connections

    Wiring / connection

    Connections that are not fully tightened or that have developed corrosion at the terminal block can cause intermittent voltage readings that the control board interprets as a false supply configuration. Inspect each terminal for secure seating and clean metal-to-metal contact.

  5. 05

    Faulty control board

    Part replacement

    If all supply wiring has been confirmed correct and the error persists, the mains monitoring circuit on the main control board may have failed. This is less common but will require board replacement to resolve.

See the test procedure for each cause

Frequently asked questions about ER 25

What does ER 25 mean on a Bosch cooktop?
ER 25 means the cooktop's control system has detected a false or incorrect mains supply connection. The unit monitors its incoming electrical supply and triggers this code when the wiring configuration does not match what the cooktop expects. This is a wiring-related fault, not a component failure, and it requires inspection of the power supply connections before the cooktop can operate safely.
Can I fix ER 25 on my Bosch cooktop myself?
Fixing ER 25 involves inspecting and correcting the high-voltage mains wiring at the terminal block and junction box, which carries serious shock risk. While a knowledgeable DIYer can visually inspect connections after confirming the breaker is off and voltage is absent at the terminals, any rewiring should be performed by a licensed electrician or appliance technician. Do not attempt to operate the cooktop while this error is active.
Is it safe to use my Bosch cooktop while ER 25 is displayed?
No, you should not use the cooktop while ER 25 is active. The error indicates the power supply is connected incorrectly, which poses a risk of electrical damage to internal components and potentially a shock or fire hazard. The cooktop should remain powered off at the circuit breaker until the wiring has been inspected and corrected by a qualified technician.
Will resetting the cooktop clear the ER 25 error?
A power reset, such as switching the circuit breaker off and back on, will not permanently clear ER 25 if the underlying wiring problem has not been corrected. The control board checks the mains supply each time the unit powers on, so the error will return immediately if the incorrect wiring configuration remains. The fault must be resolved at the supply wiring level before the code will stay cleared.
How much does it cost to repair ER 25 on a Bosch cooktop?
If the problem is simply incorrect or loose wiring at the terminal block, repair costs typically reflect electrician or technician labor only, which can range from around 75 to 200 dollars depending on your location and the complexity of the installation. If the main control board has failed and requires replacement, total repair costs including parts and labor can range from roughly 200 to 500 dollars or more. Getting a diagnostic visit from a certified technician is the best way to determine the actual scope and cost.

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