U-Line Ice Machine E4: Fourth Temperature Sensor Open
On a U-Line UONB115 or UHNP315, E4 says the fourth temperature sensor, Thermistor 4, is not sending a signal. The circuit is open, and ice production slows until it is repaired.
What does U-Line ice machine code E4 mean?
Thermistor 4, the fourth temperature sensor, is reporting open when E4 shows on a UONB115 or a UHNP315 ice machine from U-Line. Somewhere between that sensor and the board the circuit is broken, so the control gets nothing back. Ice production slows while the code is up. Clear ice machines such as the UCLR1215 do not use E4. A shorted reading from this sensor would appear as E8 instead.
E4 at a glance
- Code
- E4
- Appliance
- U-Line ice machine
- Applies to
- U-Line UONB115 and UHNP315 ice makers
- Type
- Needs attention soon
- Can you clear it yourself?
- Sometimes, after the safe checks below
- Most likely cause
- Thermistor 4 has opened up inside
What you may notice with E4
- The display holds E4 while the machine runs.
- Ice production is slower than normal.
- The bin takes longer to refill after you empty it.
- The machine runs, but results are weak.
How the ice machine detects E4
Four thermistors help the control manage the ice cycle on machines like the UONB115 and UHNP315, and the fourth is the one E4 refers to. The control feeds each sensor a small signal and reads what returns. The returned value maps to a temperature, and the cycle timing depends on it.
With Thermistor 4 open, the path is broken at some point between the sensor and the board, and no value comes back. The control flags E4 and goes on without that reading, which slows ice production as the cycle loses accuracy. Where the break lies is not visible from the outside. It could be the sensor body, a snapped lead, a plug that has lost its grip, or the board input. Since the clear ice UCLR1215 has fewer sensors, it never reports E4.
Likely causes of E4
- Thermistor 4 has opened up inside
- The lead to the fourth sensor has broken or a plug has come loose
- The board input for Thermistor 4 is not reading a signal
Can you keep using the ice machine with E4?
You may leave the machine on, but ice making will be weaker while E4 is up. The code is about a temperature reading, not about fire, gas or water, and the machine is not unsafe because of it. Keep covers closed and wires alone. If ice slows to a trickle or E4 returns after a restart, turn it off and get the circuit tested.
What you can safely check
- Turn the machine off and leave it for a minute so nothing is running.
- Power it up again and watch the display.
- Make sure nothing blocks the air around the cabinet.
- Check that the bin door is closed.
- Leave the panels in place.
- If E4 returns, that is the point to contact us.
What our technician does for E4
- Test Thermistor 4 for an open circuit
- Trace the sensor lead and connector for a break
- Check the board input for the fourth sensor
- Replace only the failed part
How to keep E4 from coming back
- Keep the area around the machine free of stacked items that trap heat.
- Move the machine gently when cleaning behind it so sensor leads stay seated.
- Check periodically that the bin door shuts without catching on the gasket.
Technical reference
- Code
- E4
- Appliance
- U-Line ice machine
- Control family
- U-Line UONB115 and UHNP315 ice makers
- Maker documentation
- U-Line owner manuals and support
- Checked
- November 2026
Code meanings come from the maker’s documentation and our own repair work; we do not reprint the maker’s document. Confirm the full model number before acting on a code. We are an independent repair company, not affiliated with U-Line Corporation.
Related U-Line ice machine error codes
E4 questions
Which U-Line machines show E4?
Models like the UONB115 and UHNP315 use E4. The clear ice UCLR1215 has fewer sensors, so E4 is not part of its code list.
How do I tell open from shorted for this sensor?
The display decides. E4 means Thermistor 4 reads open, while E8 means the same sensor reads shorted. Both leave the control without a usable fourth temperature reading.
Why not just replace the sensor?
The break may be in the lead, the plug or the board rather than the sensor. We test the circuit first, so you pay only for the part that actually failed.
Is E4 an emergency?
No. E4 reports a lost temperature reading, and the machine stays safe to leave plugged in. The main effect is less ice. Plan a repair when convenient, but do not ignore a code that keeps returning.
Does E4 mean the same as E8?
They involve the same fourth sensor but describe opposite circuit conditions. E4 is open, and E8 is shorted. The repair path starts with the same sensor circuit, but the display tells us which condition was found.
Need help with E4?
A technician finds the cause at your bar or lanai and puts the price in writing before any part comes out.