Manitowoc Undercounter Ice Machine Service Limit Lights: SL#1, SL#2, SL#3
The SL#1 light with the wrench, or SL#1, SL#2 and the wrench flashing together, report service limits: a long freeze, a long harvest, or no water sensed during freeze. Press On/Off and start a new cycle to reset. A solid red Service light needs service diagnosis.
Medium: the machine warns and may stop after repeats, and a reset is easy to try.
- Code
- SL#1 and Service (wrench) light flashing; SL#1 + SL#2 + wrench flashing for Service Limit 3
- Maker
- Manitowoc
- Equipment
- Ice machines
- Applies to
- UD/UY/UR undercounter, STH042 3/14
What does Manitowoc SL#1 and Service mean?
On Manitowoc U and UF Series undercounter machines, the control counts bad cycles and lights SL#1, SL#2 and the wrench Service light. Service Limit 1 is a long freeze: the freeze time reaches 35 to 60 minutes depending on firmware, which is 60 minutes for V1.0 to 2.53, 45 minutes for V2.54 to 2.9 and 35 minutes for UF V3.0 and later. After 3 in a row, SL#1 and the wrench flash, and after 6 the machine stops with them on solid. Service Limit 2 is a long harvest: harvest runs 3.5 then 7 minutes in total, with thaw cycles, and 3 consecutive 7-minute harvest or thaw cycles stop the machine. Service Limit 3 is 4 minutes of freeze with no water sensed: SL#1, SL#2 and the wrench flash, the control waits 30 minutes and restarts, and after 100 consecutive failures it stops with the wrench steady. There is no separate SL#3 light.
Affected models and control systems
Manitowoc U and UF Series undercounter ice machines (140, 190, 240 and 310), per the April 2025 handbook. Freeze-time limits depend on the firmware version.
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
- SL#1 and wrench lights flashing
- SL#1, SL#2 and wrench flashing together
- Machine stopped with a solid red Service light
Possible causes
Listed in Manitowoc's documentation
- Long freeze
- Long harvest, damper not opening
- No water sensed during freeze
Other likely causes — what usually sits behind SL#1 and Service on this control. A technician confirms which one it is before any part is replaced.
- Water supply shut off or restricted
- Scale on the evaporator preventing release
- Water level sensing covered by mineral deposit
Safe checks before calling for service
- Press On/Off to reset and start a new ice-making cycle.
- Check that the water supply valve is open.
- Note which lights are on and whether they are flashing or steady.
- If the machine stops with a solid Service light, call for service.
How a technician diagnoses SL#1 and Service
- Read the lights and count consecutive failures.
- Check the water supply and the water level sensing.
- Check the damper action and harvest release.
- Inspect the evaporator for scale and the sealed system pressures.
- Reset and run cycles to confirm.
- Freeze and harvest problems may come from the sealed refrigeration system.
- Damper and water circuits are close to live parts.
- Firmware version decides the limit, so the right table is needed.
How SL#1 and Service differs from similar codes
Service Limit 3 has no light of its own: it is shown by SL#1, SL#2 and the wrench together, and the count of 100 belongs to Service Limit 3.
Technical reference
- Maker documentation
- Manitowoc owner support
- Edition
- Part Number 000018622 Rev 00 04/25
- Models / control
- UD/UY/UR undercounter, STH042 3/14
- Section
- Operation, Service Limits, p.87-88
- 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 Manitowoc ice machine error codes
What resets a service limit?
Press On/Off and start a new ice-making cycle.
Why do freeze limits differ?
They depend on the firmware version.
What does a solid Service light mean?
The machine stopped and needs service diagnosis.
Need help with Manitowoc SL#1 and Service?
A technician confirms the cause on site and gives you the price in writing before any work starts.