Alto-Shaam Combi Oven Error Code E40: B3 Probe Shorted
E40 B3 Fault means probe B3, the condenser water probe, is shorted to ground. Press the Start icon to acknowledge it, and ask a technician to check the probe and its wiring.
Medium: steam condensing cannot be monitored until the probe circuit is repaired.
- Code
- E40
- Maker
- Alto-Shaam
- Equipment
- Combi ovens
- Applies to
- Combitherm CT PROformance (CTP) and CT Classic (CTC)
What does Alto-Shaam error code E40 mean?
Probe B3 measures the condenser water temperature. A temperature probe has two leads, and the control reads the small current passing through it. If one lead touches ground, the reading collapses to an impossible value and the control posts E40 B3 Fault. The manual says that the probe is shorted to ground and has one listed cause: the probe is miswired or has malfunctioned. A short is different from a disconnected probe. A disconnected B3 gives E25, while a short gives E40. The cause can be a pinched wire, a damaged lead or moisture across the contacts, though the manual itself only lists the miswire or failed probe. Pressing Start acknowledges the message and the oven then tries to return to normal operation, but the shorted circuit stays until it is repaired, so the control cannot judge the condenser water correctly.
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 condenser probe B3.
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
- E40 B3 Fault on the display
- Condenser cooling behaving oddly during steam
- Steam venting hot at the drain
Possible causes
Listed in Alto-Shaam's documentation
- Probe B3 miswired or failed
Other likely causes — what usually sits behind error code E40 on this control. A technician confirms which one it is before any part is replaced.
- A lead insulation worn through where it touches the condenser housing
- Water at the probe fitting bridging the two contacts
Safe checks before calling for service
- Press the Start icon once to acknowledge E40.
- Look under and behind the oven for water leaks near the condenser area, without removing panels.
- Avoid steam programs until the probe is checked.
- If E40 returns, note whether E25 or E15 appeared earlier.
How a technician diagnoses error code E40
- Read the code and check history for E25 or E15.
- Inspect the B3 probe and wiring for abrasion, pinching and moisture.
- Disconnect B3 and measure resistance from each lead to ground.
- Compare the probe's resistance with its chart.
- Replace the probe or repair the wire where the short is found.
- The probe is part of a live control circuit at the condenser.
- Finding a short to ground needs isolating the lead and measuring to chassis.
- Steam venting without condenser monitoring can send very hot water to the drain.
How error code E40 differs from similar codes
E25 reports B3 defective or disconnected, E15 reports condenser water above 212 F (100 C), and E40 reports B3 shorted to ground.
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
Is E40 the same as E25?
No. E25 is an open or defective B3, E40 is a short to ground.
Will E40 clear on its own?
Only if a wet connection dries out; a shorted lead stays.
Does E40 mean the water is too hot?
No, it says the probe circuit is shorted.
Need help with Alto-Shaam error code E40?
A technician confirms the cause on site and gives you the price in writing before any work starts.