Alto-Shaam Combi Oven Error Code E109: High Limit Switch Open
E109 High Limit Switch means the high limit switch input to the control board (N7) is open. Press the high limit reset switch once only, and if the message stays, call a service provider.
High: the high limit has opened and the oven should not run until the cause is found.
- Code
- E109
- Maker
- Alto-Shaam
- Equipment
- Combi ovens
- Applies to
- Combitherm CT PROformance (CTP) and CT Classic (CTC)
What does Alto-Shaam error code E109 mean?
The high limit switch is the oven's independent protection against overheating. It sits in the heating circuit and opens when temperatures rise too far. The control board watches its input, called N7. When the switch is open, the control posts E109 High Limit Switch and the heat cannot run. The manual gives a firm instruction: press the high limit reset switch once only. If the condition remains, call for service. The five causes listed are an overheat condition, a cooling fan malfunction, a heat relay stuck closed, a defective connection from the high limit switch to the control board, and the high limit switch itself. Pressing the reset repeatedly will not help and may hide an overheating cause, so the manual limits it to one press. The first four causes lead to real overheating or a wiring problem; only the last two are the switch itself.
Affected models and control systems
The full CT PROformance and CT Classic range, 6-10 up to 20-20, electric and gas, where the high limit switch feeds the N7 input on the control board.
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
- E109 High Limit Switch on the display
- Oven not heating
- Hot oven that will not restart
Possible causes
Listed in Alto-Shaam's documentation
- Overheat condition
- Cooling fan malfunction
- Heat relay stuck closed
- Defective high limit switch connection to the control board
- High limit switch malfunction
Other likely causes — what usually sits behind error code E109 on this control. A technician confirms which one it is before any part is replaced.
- A heating contactor welded closed so the element keeps heating past the setpoint
- A slow-running cooling fan letting the control area overheat
Safe checks before calling for service
- Let the oven cool completely.
- Press the high limit reset switch once, and only once.
- Start a short program to see whether it runs normally.
- If E109 returns, do not press reset again; turn the oven off and call.
How a technician diagnoses error code E109
- Read the code and ask whether the oven ran hot beforehand.
- Check the cooling fan and its airflow.
- Check the heat relay or contactor for sticking.
- Measure the continuity of the high limit switch and its wiring to N7.
- Replace the part that fails the test, never bypass the switch.
- A high limit exists to stop overheating, so it must never be jumped or reset repeatedly.
- Heat relays and the heating circuit carry live 208-240 V.
- Finding why the limit tripped needs measuring temperatures and relay states.
How error code E109 differs from similar codes
E02 and E108 report relay board temperature; E109 reports the high limit switch input open.
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
How often may I press reset?
Once. If the message stays, call.
Is the high limit a safety device?
Yes, so it must not be bypassed.
Can a loose wire cause E109?
Yes, a defective connection to the control board is a listed cause.
Need help with Alto-Shaam error code E109?
A technician confirms the cause on site and gives you the price in writing before any work starts.