Alto-Shaam Combi Oven Error Code E42: B5 Probe Shorted
E42 B5 Fault means probe B5, the bypass steam temperature probe, is shorted to ground. Press the Start icon to acknowledge it, and ask a technician to check the probe and its leads.
Medium: steam handling cannot be monitored until the short is cleared.
- Code
- E42
- Maker
- Alto-Shaam
- Equipment
- Combi ovens
- Applies to
- Combitherm CT PROformance (CTP) and CT Classic (CTC)
What does Alto-Shaam error code E42 mean?
Probe B5 measures steam temperature in the bypass path. The control expects a signal inside a normal range for a temperature probe. When the circuit instead reads as shorted to ground, it posts E42 B5 Fault. The manual states the meaning plainly and lists a single cause, that the probe is miswired or has malfunctioned. This differs from E24, which reports B5 as defective or disconnected, so E42 sends the technician to look for a lead touching metal rather than a break. The bypass runs close to hot steam, so the lead insulation and connector are the first places to look. Pressing Start acknowledges the message and the oven then tries to return to normal operation, but the reading does not recover until the short is cleared, and steam cycles that rely on bypass temperature may not behave correctly in the meantime.
Affected models and control systems
Alto-Shaam Combitherm CT PROformance and CT Classic combi ovens in sizes 6-10, 10-10, 7-20, 10-20, 20-10 and 20-20, electric and gas, with bypass probe B5.
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
- E42 B5 Fault on the display
- Steam cycles starting then stopping
- Bypass temperature missing from the readout
Possible causes
Listed in Alto-Shaam's documentation
- Probe B5 miswired or failed
Other likely causes — what usually sits behind error code E42 on this control. A technician confirms which one it is before any part is replaced.
- A connector corroded by steam creating a path to ground
- A lead trapped between the bypass hose clamp and a metal bracket
Safe checks before calling for service
- Press the Start icon once to acknowledge E42.
- Check for steam or condensation escaping around the back of the oven.
- Do not open covers to look for the probe.
- If E42 returns, record the program in use and mention E24 if it appeared before.
How a technician diagnoses error code E42
- Read the code and check history for E24.
- Inspect B5 and its lead where it runs near the bypass hose.
- Disconnect B5 and measure resistance from each lead to ground.
- Compare the probe's resistance to its chart.
- Repair the insulation or replace B5 depending on where the short lies.
- The probe sits in a hot steam path and its leads reach a live control board.
- An intermittent short may only show up when the oven is hot and wet.
- Replacing the probe requires cooling and panel removal.
How error code E42 differs from similar codes
E24 reports B5 defective or disconnected, while E42 reports it shorted to ground; E40, E41 and E43 are the same short on other probes.
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)
- 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
What is the bypass?
The path that carries steam out of the cavity toward the condenser.
Can E42 appear with E40?
Yes, if moisture or damage affects more than one probe circuit.
Will pressing Start fix it?
It acknowledges the message but cannot remove a short.
Need help with Alto-Shaam error code E42?
A technician confirms the cause on site and gives you the price in writing before any work starts.