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Error code reference

Bosch Cooktop Error Code ER 26

Relay supply voltage too high in the off state of control.

Bosch codesBosch cooktop codes

Relay supply voltage too high in the off state of control.

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What ER 26 means on a Bosch cooktop

ER 26 on a Bosch cooktop indicates that the relay supply voltage is reading too high during the off state of the control board. In normal operation, the relay circuit should measure a low or near-zero voltage when the control is switched off, because the relay is not energized and the circuit is open. When the control electronics detect voltage present on the relay supply line despite the control being in an off state, the system flags this as an abnormal condition and triggers ER 26 to protect components from potential damage.

This fault points directly to the relay driver circuit on the main control board or the power supply section feeding the relay coils. The most common sources include a failing relay that has welded contacts or a shorted coil, a defective triac or switching component on the control board that is leaking voltage even when commanded off, or a wiring fault that is introducing voltage onto the relay supply line through an unintended path. In some cases, a failing power supply filter capacitor can cause voltage to remain elevated on the relay rail after shutdown.

Because this error involves relay control circuitry, it carries implications for the safe operation of the cooktop. A relay that cannot be reliably switched off may result in a heating element remaining energized unintentionally. The control board is typically the primary suspect, though inspecting wiring harness integrity and relay condition should be part of any complete diagnosis before replacing components.

Source: manufacturer service documentation.

Common causes of ER 26

  1. 01

    Faulty main control board

    Part replacement

    A defective switching component such as a triac or relay driver transistor on the control board can leak voltage onto the relay supply line even when the control is in the off state. This is the most frequent root cause of ER 26 and typically requires control board replacement.

  2. 02

    Welded or shorted relay contacts

    Part replacement

    A relay with fused or welded contacts can create a feedback path that registers abnormal voltage on the supply line. Inspect the relay for signs of overheating or carbon scoring, and test coil resistance for shorts.

  3. 03

    Wiring harness fault or short

    Wiring / connection

    Damaged insulation or a pinched wire in the relay supply harness can create an unintended voltage path to the relay circuit. Visually inspect all wiring connected to the control board and relay assembly for chafing, burns, or contact with chassis metal.

  4. 04

    Failing power supply filter capacitor

    Part replacement

    A degraded filter capacitor on the relay power supply rail may fail to discharge properly after shutdown, leaving residual voltage that the control interprets as an overvoltage fault. This is typically identified through board-level inspection or component testing.

See the test procedure for each cause

Frequently asked questions about ER 26

What does ER 26 mean on a Bosch cooktop?
ER 26 means the cooktop has detected that the relay supply voltage is too high while the control is in the off state. Normally, the relay circuit should show little to no voltage when not energized. This fault is flagged by the control electronics to prevent unsafe operation and potential component damage. It points to an issue with the control board, relay assembly, or associated wiring.
Can I fix ER 26 on my Bosch cooktop myself?
Diagnosing ER 26 requires safely accessing the control board and relay components, which involves working near line-voltage wiring. A knowledgeable DIYer comfortable with appliance electronics can inspect wiring harnesses for visible damage, but testing relay coil resistance and identifying board-level component failures typically requires a multimeter and experience with control board diagnostics. If the control board or relay needs replacement, a qualified technician is recommended.
Is it safe to use my Bosch cooktop when ER 26 is displayed?
You should not continue using the cooktop while ER 26 is active. This fault indicates abnormal voltage in the relay circuit during the off state, which could mean a relay is not switching off correctly. Continuing to operate the unit risks a heating element remaining energized unintentionally, which is a safety hazard. Disconnect power until the fault is diagnosed and repaired.
Will resetting the cooktop clear the ER 26 error?
Resetting the cooktop by cutting power at the breaker and restoring it may temporarily clear the display, but ER 26 will return if the underlying fault in the relay circuit or control board is still present. A reset does not repair a welded relay, a leaking switching component, or a wiring fault. Persistent recurrence of ER 26 after a reset confirms that a component repair or replacement is needed.
How much does it cost to repair a Bosch cooktop showing ER 26?
Repair costs vary depending on the root cause. A wiring harness repair may cost between $75 and $150 in labor if no parts are needed. Control board replacement on a Bosch cooktop typically runs between $200 and $450 including parts and labor, depending on the model. Relay replacement alone is generally less expensive, often in the $100 to $250 range with a service call included.

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