Convotherm Combi Oven Error Code E21.0: Oven Sensor Open Circuit
E21.0 on the older Convotherm OES, OEB, OGS and OGB ovens means the oven sensor (B6) has an open circuit. The manual's only response is to contact customer service. Switch the oven off until a technician checks it.
High: without the oven sensor the control cannot regulate temperature, so heating stops.
- Code
- E21.0
- Maker
- Convotherm
- Equipment
- Combi ovens
- Applies to
- Convotherm OES / OEB / OGS / OGB (older, pre-C4)
What does Convotherm error code E21.0 mean?
Sensor B6 is the oven sensor, which reports the cooking chamber temperature to the control. The control reads it as a resistance through a small circuit and expects a value inside a sensible range. An open circuit means that circuit is broken: a wire has come apart, a plug has worked loose, or the sensor itself has failed. The control then sees no signal at all and shows E21.0. Without a temperature reading the control cannot hold the chamber at the set value, and it cannot tell whether heating is safe, so it stops heating. The manual gives only one response, to contact customer service. That makes sense, because an open circuit cannot be repaired from the front of the oven. The most helpful thing an operator can do is to keep notes about what the oven was doing when the code appeared.
Affected models and control systems
Older Convotherm combi ovens in the OES, OEB, OGS and OGB line, which came before the C4. The source is that line's English user manual, a translation of the original, with no revision number printed.
Code numbers and their meaning can change between control generations. We match the full model and control before acting on a code.
What you may notice
- E21.0 on the display
- Oven stops heating
- Chamber temperature shows no value or an odd one
- Oven works briefly after a restart, then stops again
Possible causes
Likely causes — what usually sits behind error code E21.0 on this control. A technician confirms which one it is before any part is replaced.
- Wire to the oven sensor broken or burned
- Sensor plug loose at the connector
- Sensor failed open
- Cable damaged during a past repair or cleaning
Safe checks before calling for service
- Switch the oven off and let it cool.
- Do not pull on cables behind the oven or open the panels.
- Restart once to see if the message goes away.
- Contact customer service as the manual instructs.
- Note whether the display ever showed a chamber temperature before the code appeared.
How a technician diagnoses error code E21.0
- Read E21.0 and the history to see whether it appears at once or after heating.
- Measure sensor B6 resistance at the sensor and compare it with its temperature.
- Check continuity of the cable and connector from the sensor to the board.
- Inspect the plug at the board for looseness or corrosion.
- Replace the sensor or cable as the tests show.
- Run a heat-up test and confirm that the chamber holds the set temperature.
- The sensor circuit is tested with a meter close to line-voltage parts.
- A cable that fails only when hot needs the oven heated and watched while it is measured.
- The sensor sits in the cooking chamber, and reaching its wiring may mean taking panels off a heavy oven.
How error code E21.0 differs from similar codes
E21.1 is the same sensor reporting a ground fault instead of an open circuit.
Technical reference
- Maker documentation
- Convotherm owner support
- Edition
- No revision/part number found in the text read
- Models / control
- Convotherm OES / OEB / OGS / OGB (older, pre-C4)
- Section
- Troubleshooting, Errors and required responses, pp. 161-162
- Checked
- October 2026
We use the maker's document to read the code and do not reproduce it. Always confirm the complete model and control before applying these steps.
Related Convotherm combi oven error codes
What does open circuit mean here?
The electrical path to the sensor is broken, so the control gets no reading at all.
Can I use the oven at a fixed setting?
No. The control needs the sensor to regulate heat, so it stops heating.
Is B6 the core probe?
No. B6 is the oven sensor in the chamber. The core probe codes are E12.x and E22.x.
Need help with Convotherm error code E21.0?
A technician confirms the cause on site and gives you the price in writing before any work starts.