Alto-Shaam Combi Oven Error Code E23: B4 Steam Generator Probe
E23 B4 Steam Generator Probe Fault means the temperature probe in the steam generator, B4, is defective or not read correctly. Press the Start icon to acknowledge it, and have a technician check B4 and its wiring.
Medium: steam cooking is affected while the generator probe cannot be read.
- Code
- E23
- Maker
- Alto-Shaam
- Equipment
- Combi ovens
- Applies to
- Combitherm CT PROformance (CTP) and CT Classic (CTC); Combitherm CT Express / ESi / CCi (older 4-10 and 4.10 units; boiler or generator electric/gas)
What does Alto-Shaam error code E23 mean?
Probe B4 reports the steam generator's temperature to the control. That reading protects the generator, because E13 is posted when B4 climbs above 248 F (120 C). The control also checks the probe itself. If the reading shows B4 open, shorted or wired wrong, the control posts E23 B4 Steam Generator Probe Fault. The manual lists two causes: the B4 probe has failed, or it is miswired. A miswire usually follows a repair or part replacement, which makes it worth asking whether anyone worked on the oven recently. Pressing Start acknowledges the message and the oven then tries to return to normal operation, but the generator cannot be monitored while B4 is not readable, so steam programs may be blocked. Without that protection a scaled or overheated generator would go unnoticed.
Affected models and control systems
The CT PROformance and CT Classic family: 6-10, 10-10, 7-20, 10-20, 20-10 and 20-20, electric and gas. A CT Express manual describes this as a B4 boiler probe error.
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
- E23 B4 Steam Generator Probe Fault on the display
- Steam programs not starting
- Generator temperature missing or implausible on the screen
Possible causes
Listed in Alto-Shaam's documentation
- B4 probe malfunction
- B4 probe miswired
Other likely causes — what usually sits behind error code E23 on this control. A technician confirms which one it is before any part is replaced.
- A probe wire damaged by heat where it passes close to the generator housing
- Probe connector corroded by steam leakage around the generator
Safe checks before calling for service
- Press the Start icon once to acknowledge E23.
- Avoid steam programs until the oven has been checked; dry heat programs may still be available.
- Note whether any repair or part replacement was done on the oven just before the code appeared.
- Give the technician the date of the last descale.
How a technician diagnoses error code E23
- Read the code and ask about recent repairs that could have disturbed wiring.
- Inspect B4 and its wiring path for damage, with the oven cool.
- Verify the connection against the wiring diagram.
- Measure the B4 resistance against its chart at a known temperature.
- Replace the probe only after the wiring is confirmed correct.
- B4 is mounted on the steam generator, which stays very hot.
- The probe's wiring runs to the control board with live voltage nearby.
- Resistance testing requires isolating the probe from the circuit.
How error code E23 differs from similar codes
E13 means B4 is working and reads too hot; E23 means B4 cannot be read properly.
Technical reference
- Maker documentation
- Alto-Shaam owner support
- Edition
- MN-35949 Rev 08 03/22
- Models / control
- Combitherm CT PROformance (CTP) and CT Classic (CTC); Combitherm CT Express / ESi / CCi (older 4-10 and 4.10 units; boiler or generator electric/gas)
- Section
- Error Codes, pp. 25-31
- 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 Alto-Shaam combi oven error codes
Is E23 the same as E13?
No. E13 is a working B4 reading above 248 F (120 C); E23 is a defective or miswired probe.
Can steam cooking continue?
Not safely, since the oven cannot monitor the generator.
Does descaling fix E23?
Not directly, because the manual lists only a failed or miswired probe.
Need help with Alto-Shaam error code E23?
A technician confirms the cause on site and gives you the price in writing before any work starts.