Bunn Slush Machine TEMPERATURE SENSOR SHORTED: Thermistor Circuit
TEMPERATURE SENSOR SHORTED points to the thermistor that reads barrel temperature, or the wiring between it and the control board. Without a believable reading the machine cannot decide when to freeze, and the barrel may stop cooling. Check that product is above the minimum fill line, leave the wiring alone, and call us if the message stays on.
Medium: the barrel may stop cooling until the sensor circuit is repaired.
- Code
- TEMPERATURE SENSOR SHORTED
- Maker
- BUNN
- Equipment
- Slush & frozen drinks
- Applies to
- ULTRA-1 / ULTRA-2 frozen drink dispenser
What does BUNN TEMPERATURE SENSOR SHORTED mean?
The control on an ULTRA-1 or ULTRA-2 reads the barrel thermistor as a resistance. A short means the resistance has fallen to near zero, which would be a temperature far outside what a barrel can reach. The control knows this is not real, so it flags TEMPERATURE SENSOR SHORTED and stops trusting the sensor. This is a different state from OPEN. Here the circuit is connected, but something has made it look closed: wires touching each other, insulation worn through, a connector with moisture across its pins, or an input on the board that has failed. With no temperature to work from, the control cannot judge when to run the compressor and when to rest, so the barrel can stop cooling and the quality of the product suffers. The message stays on until the sensor circuit is repaired, because it is not a condition that reset or time can clear.
Affected models and control systems
This page covers the older Bunn ULTRA-1 and ULTRA-2 frozen drink dispensers.
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
- TEMPERATURE SENSOR SHORTED shows on the display
- The affected barrel stops cooling or freezes unevenly
- Message stays on after the machine is switched off and on
Possible causes
Listed in BUNN's documentation
- Damaged wiring between the thermistor and the control board
- A shorted thermistor circuit
- A damaged connector at the control board
- A failed control board input
Other likely causes — what usually sits behind TEMPERATURE SENSOR SHORTED on this control. A technician confirms which one it is before any part is replaced.
- A harness section rubbed through where it passes the frame, so two conductors touch
- Sugar and moisture across the pins of the thermistor connector after a spill
- A thermistor that has failed internally and reads as a dead short
Safe checks before calling for service
- Note the message and which barrel it applies to.
- Check that product is above the minimum fill line.
- Leave the back panel closed and the wiring alone.
- If the message stays on, turn the machine off and call us.
How a technician diagnoses TEMPERATURE SENSOR SHORTED
- Read the display and confirm the barrel.
- Inspect the thermistor wiring and connector for pinching, rub marks and moisture.
- Disconnect the thermistor at the plug and check its resistance against the barrel temperature.
- Check the board input with the sensor disconnected.
- Replace the thermistor, harness or board only after the readings show which part is out.
- The shorted wiring is inside the machine and can be anywhere along the harness, so it takes a meter and panel removal to find.
- Testing the connector and the control board input means working near live wiring.
- With no real temperature, the barrel cannot be managed, so it is best not to keep serving from it.
How TEMPERATURE SENSOR SHORTED differs from similar codes
TEMPERATURE SENSOR OPEN is the opposite reading, where the control sees no connection. It can come from a low barrel; a short cannot.
Technical reference
- Document
- ULTRA-1/ULTRA-2 Service & Repair Manual 41084.0000D, Troubleshooting p.19-21
- Maker documentation
- BUNN owner support
- Edition
- 41084.0000D 03/13 (copyright 2009 Bunn-O-Matic Corporation)
- Models / control
- ULTRA-1 / ULTRA-2 frozen drink dispenser
- Section
- Troubleshooting flowcharts: Torque Sensor Error p. 19, Temperature Sensor Error p. 20, Clean Filter Messages p. 21
- 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 BUNN slush & frozen drink error codes
Can I keep running the machine with TEMPERATURE SENSOR SHORTED on?
It is not advisable. The control has no real temperature, so the barrel may stop cooling.
Will adding product clear it?
Unlike the open message, a short is not caused by a low barrel, so adding product is unlikely to clear it.
Does this mean I need a new control board?
Not always. The thermistor, wiring and connector are checked first, because they are more common.
Need help with BUNN TEMPERATURE SENSOR SHORTED?
A technician confirms the cause on site and gives you the price in writing before any work starts.