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Error code reference

Bosch Cooktop Error Code ER 24

Wrong number of relays detected.

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Wrong number of relays detected.

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What ER 24 means on a Bosch cooktop

ER 24 on a Bosch cooktop indicates that the control system has detected an incorrect number of relays during its internal diagnostic cycle. The cooktop's main control board continuously monitors the relay configuration to confirm that the number of active relays matches what is expected for the specific model. When this count does not match the expected value, the board flags ER 24 and typically shuts down heating functions to prevent unsafe operation.

Relays on an induction or electric cooktop are responsible for switching power to the individual heating zones or boost circuits. Each zone may use one or more relays, and the control board identifies these components at startup or during operation through feedback signals. A mismatch can occur when a relay fails in an open or closed position, when the control board itself develops a fault affecting relay detection circuitry, or when there is a wiring issue between the relay assembly and the control board.

Because this error points directly to the relay count verification process, diagnosis centers on the relay board or relay cluster, the wiring harness connecting relays to the main control board, and the main control board itself. Physical inspection for burned contacts, failed solder joints, or damaged wiring is the appropriate starting point. In many cases, either a faulty relay board or a failed main control board is the root cause, and the defective component will need replacement to clear the fault.

Source: manufacturer service documentation.

Common causes of ER 24

  1. 01

    Failed or stuck relay on the relay board

    Part replacement

    One or more relays may have failed in an open or welded-closed position, causing the control board's relay count to come up short or read incorrectly. Inspect the relay board for signs of burning, discoloration, or damaged contacts.

  2. 02

    Faulty main control board

    Part replacement

    The main control board may have developed a fault in the circuitry responsible for detecting and counting relays, causing it to report an incorrect number even when the relays themselves are intact. This typically requires replacement of the control board.

  3. 03

    Damaged or loose wiring harness

    Wiring / connection

    A disconnected, pinched, or damaged wiring harness between the relay assembly and the control board can interrupt the feedback signals the board uses to count relays. Inspect all connectors and wire runs for visible damage or loose pins.

  4. 04

    Relay board connector corrosion or poor contact

    Wiring / connection

    Corrosion or debris on the connector pins linking the relay board to the main control board can cause intermittent or missing signals, leading to an incorrect relay count. Cleaning or reseating the connectors may resolve the issue if no physical damage is present.

See the test procedure for each cause

Frequently asked questions about ER 24

What does ER 24 mean on a Bosch cooktop?
ER 24 means the cooktop's control board has detected a wrong number of relays during its internal diagnostic check. Relays are the switching components that control power to each cooking zone, and the board expects a specific count based on the model. When that count is off, the board triggers ER 24 and typically disables heating to prevent unsafe operation. The fault usually points to a failed relay, a faulty control board, or a wiring issue.
Can I fix ER 24 on my Bosch cooktop myself?
Some aspects of diagnosis, such as checking for loose connectors or reseating wiring harnesses, can be done by a careful DIYer with experience working on appliances. However, replacing a relay board or main control board involves working near high-voltage components and requires proper safety precautions, including disconnecting power at the breaker before opening the unit. If you are not comfortable with appliance electronics repair, a qualified technician is the safer option.
Is it safe to keep using my Bosch cooktop with ER 24 displayed?
No, you should not continue using the cooktop while ER 24 is active. The error indicates that the control board cannot confirm the relay configuration is operating correctly, which means heating zones may behave unpredictably. Continuing to use the appliance in this state could pose a safety risk and may cause additional damage to other components.
Will resetting my Bosch cooktop clear the ER 24 error?
A power reset, done by switching off the circuit breaker for 30 to 60 seconds and then restoring power, may temporarily clear the error if it was caused by a transient control board glitch. However, if the underlying cause is a physically failed relay or damaged wiring, the error will return after the reset. A permanent fix requires identifying and replacing the faulty component.
How much does it cost to repair ER 24 on a Bosch cooktop?
Repair costs depend on which component is at fault. A relay board replacement typically runs in the range of $100 to $250 for parts, while a main control board can cost $150 to $400 or more depending on the model. Adding professional labor, total repair costs commonly fall between $200 and $550. Getting a diagnosis from a technician before ordering parts is advisable to avoid purchasing the wrong component.

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