Thermador Masterpiece wall oven Error Code E303: Meaning & How to Fix It

By the ErrorCodePro Editorial Team · Last reviewed October 20, 2026

Thermador Masterpiece wall oven error code E303 means: Electronic oven control board too hot. The electronic oven control board temperature exceeded 212 degrees. [1] Keep using it? No. Stop using it until the cause is fixed. Start with the owner checks below, beginning with: write down the code and model number.

Source: Thermador Masterpiece wall oven error-code chart, via Sears PartsDirect [1].

Quick facts

Code	E303
Also shown as	None listed by the manufacturer
Brand / appliance	Thermador Masterpiece wall oven
System	Heating
Meaning (service chart)	Electronic oven control board too hot. The electronic oven control board temperature exceeded 212 degrees. [1]
Keep using it?	No. Stop using it until the cause is fixed
DIY-safe?	Owner checks only (listed below)
Support	Thermador customer support (see your owner's manual)
Source document	Thermador Masterpiece wall oven error-code chart (via Sears PartsDirect)

On this page: Meaning · Steps · Parts · When to call a technician · Related codes · FAQ

What error code E303 means on a Thermador Masterpiece wall oven

Electronic oven control board too hot. The electronic oven control board temperature exceeded 212 degrees. [1]

This is a heating code. Codes and wording can vary by model, so check your owner's manual for your model number.

How to fix Thermador Masterpiece wall oven error code E303 (safe owner checks)

Safety first: disconnect power before you remove any panel or reach into the sump or drum. Do not touch wiring, the control board or the motor. If you see water near electrical parts, stop and call a technician. These steps are based on the Thermador Masterpiece wall oven error-code chart (via Sears PartsDirect) [1], rewritten for clarity.

Write down the code and model number. Note exactly what the display shows (E303) and copy the full model number from the rating label, so you can confirm this chart applies to your masterpiece wall oven and order the right parts.
Close the door or lid fully. Make sure the upper oven door closes fully.
Do a power reset. Unplug the appliance or switch off its breaker for one minute, then restore power and try again. If the code clears and stays away, it may have been a one-off fault.
Test and decide. Run a short cycle or restart and watch the display. If E303 comes back after these checks, stop using the range for this function and call a technician, because the remaining causes need meters or part replacement.

The first and last steps (and the power reset) are general owner checks added by ErrorCodePro; the rest follow the Thermador Masterpiece wall oven error-code chart published by Sears PartsDirect, rewritten for safe owner use.

Parts that may be involved

Exact parts depend on your model number. This page lists part types only, never part numbers.

Upper oven cooling fan
Upper oven door seal
Upper oven door hinges
Wire harness

When to call a technician

Technician: replace the upper oven door hinges if defective.
Technician: check the upper oven door seal and replace the seal if damaged.
Technician: check the upper cooling fan wire harness connections.
Reconnect any loose wires or replace the wire harness if damaged.
Technician: replace the upper oven cooling fan if it doesn't run when activated.
Anything involving wiring, the control board, the motor or the water valve electrics
The appliance is under warranty: contact Thermador customer support (see your owner's manual) first

Frequently asked questions

What does error code E303 mean on a Thermador Masterpiece wall oven?

The Thermador Masterpiece wall oven error-code chart lists E303 as follows: Electronic oven control board too hot. The electronic oven control board temperature exceeded 212 degrees.

Is it safe to keep using the Masterpiece wall oven with E303?

No. Stop using it until the cause is fixed.

Can I fix Thermador Masterpiece wall oven error E303 myself?

Only with the owner checks on this page, starting with: write down the code and model number. If it persists, call a technician or Thermador customer support (see your owner's manual).

Sources

Sears PartsDirect: Thermador Masterpiece wall oven error-code chart (third-party copy of manufacturer service data)

Last reviewed: October 20, 2026. ErrorCodePro is not affiliated with Thermador.