Safety first: Disconnect power at the breaker and close the water supply.

Confirm symptom: Run a hot cycle and open the door immediately after it ends. If the interior and dishes are cold and E09 is shown, the heater is likely not working.
Access heater assembly: Remove the toe-kick and side panel to access the flow-through heater/heat pump assembly mounted under the tub.
Check wiring: Inspect heater terminals and connectors for discoloration, burning, or looseness. Reseat connectors firmly.
Measure heater resistance: Disconnect the heater and measure resistance with a multimeter. An open circuit indicates a failed heater. Compare reading to Bosch specifications.
Inspect for leaks: Look for signs of water leakage around the heater, which can cause corrosion and failure.
Replace heater assembly: If the heater is open or damaged, replace the complete Bosch heat pump/flow-through heater assembly. Transfer hoses and clamps carefully and ensure all seals are tight.

Dishwasher completes cycles but dishes are cold and wet; E09 displayed at or near end of cycle.

Possible Causes