Gaggenau Microwave Combi Oven: error code E138

Professional Repair Guide

What is this symptom?

If your Gaggenau Microwave Combi Oven displays error code E138 when trying to start a heating cycle, it indicates a potential communication fault or power supply issue. This error can disrupt normal operation and needs to be addressed promptly to restore functionality.

Urgency: Medium

Important Tips for Gaggenau Models

Official documentation for error code E138 is not readily published by Gaggenau; contacting Gaggenau support with the exact model number is recommended for accurate diagnostics.

Possible Causes

Communication fault between control board and inverter/high-voltage section

How to Identify: Error code appears immediately on starting a heating cycle; no heating occurs.

Part: Control board / Inverter board

Power supply or voltage issues

How to Identify: Error only appears when power draw increases (e.g., start of heating; outlet voltage irregular.

Part: Power supply wiring/outlet

DIY Solutions

Power reset of the microwave

Easy 30-60 minutes (including disconnect)

Unplug the microwave from the mains or turn off the circuit breaker.
Wait at least 30 minutes to allow internal capacitors to discharge and reset electronics.
Restore power and attempt to start a heating cycle again.

⚠️ Safety First: Ensure the unit is fully powered off before unplugging.

Check external power and outlet

Easy 10-15 minutes

Tools Needed: Outlet tester or another appliance

Unplug the microwave and test the outlet with another appliance to confirm proper voltage.
If voltage irregularities are suspected, try plugging the microwave into a known good outlet.

⚠️ Safety First: Do not work on electrical outlets without proper knowledge or safety precautions.

Next step

Choose the next step for error code E138

Confirm the diagnosis before ordering. An error code can identify the system involved, but it does not prove that a specific part has failed.

Diagnostic aid

Optional aid — no replacement part was confirmed

Digital Multimeter

Essential tool for diagnosing electrical continuity, voltage, and resistance problems.

No purchase link is shown because the diagnosis is not specific enough to recommend a product.

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Professional Repairs

Inspect and repair/replace control board or inverter board

Estimated Cost: $250 - $600

When to Call a Professional

Error E138 persists after power reset and outlet checks

Visible signs of electronic component damage (burnt board, swelling capacitors)

The unit fails to heat and beeps or shuts down immediately on start

Preventive Maintenance

Power cycling occasionally: Temporary communication glitches in control electronics
Frequency: as needed
Keep vents clear and clean: Overheating that may contribute to electronic faults
Frequency: monthly

Frequently Asked Questions

Why is my Gaggenau Microwave Combi Oven error code E138?

Error code E138 may indicate a communication fault between the control board and inverter or power supply issues.

How do I fix Gaggenau Microwave Combi Oven error code E138 myself?

Try a power reset by unplugging the microwave for 30 minutes or checking the outlet for proper voltage.

How much does it cost to fix error code E138?

Professional repairs for error code E138 typically range from $250 to $600.

When should I call a technician for error code E138?

If DIY solutions don't resolve the issue, or if you're uncomfortable inspecting internal components, contact a technician.

Community Analytical Insights

Analysis based on real user discussions from appliance repair communities

Can I Fix This Myself?

70%

DIY Success Rate Difficulty: Either

Common Issues Reported by Users

Faulty door switch preventing microwave operation
Malfunctioning control board causing error code
Overheating due to blocked ventilation or cooling system failure

User Suggested Solutions

Check and replace the door switch: Unplug the microwave, remove the outer cover, locate the door switch, test with a multimeter, and replace if faulty.
Inspect and reset the control board: Unplug the oven, access the control board, check for visible damage or burnt components, and reset or replace if necessary.
Ensure proper ventilation: Check that the vents are not blocked, clean any dust or debris, and ensure the cooling fan is operational.