UniMac Commercial Dryer Error Code SH: Shorted Thermistor
SH on a UniMac 120 or 170 lb dryer means the control sees the thermistor circuit as shorted, which it reads as an extreme temperature. Turn the dryer off, let the drum cool and clean the lint screen. Call us to test the circuit.
Medium: the dryer stops heating, but it stops safely and nothing is at immediate risk.
What does UniMac error code SH mean?
The thermistor is the dryer's temperature sensor, and the control reads its resistance as heat. When the circuit is shorted, the resistance collapses toward zero. The control interprets that as an extreme temperature reading, though the drum is not necessarily hot. SH stands for shorted. Pinched wiring, a damp or corroded connector, or a failed thermistor can all create that short. With a reading it cannot believe, the control stops heating, because it cannot tell whether the dryer is cold or dangerously hot. If the drum is cool to the touch yet SH shows, that points to the circuit and not to the real temperature. The open-circuit twin of this code is OP, which means a broken wire or unplugged sensor instead.
Affected models and control systems
This applies to UniMac 120 and 170 lb tumble dryers with the On Premise Micro control, such as the UA120L, in the TMB1268C troubleshooting family.
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
- SH on the display
- Dryer refusing to heat
- Drum that feels cool even though the control reports extreme heat
Possible causes
Listed in UniMac's documentation
- Wiring insulation near the thermistor
- Moisture or corrosion at the connector
- The thermistor itself
- Control input for the thermistor
Other likely causes — what usually sits behind error code SH on this control. A technician confirms which one it is before any part is replaced.
- A wire pinched under a panel edge after a past repair
- Steam or detergent vapor corroding the connector in a damp laundry room
- A thermistor tip that touched metal and grounded the circuit
Safe checks before calling for service
- Turn the dryer off, then give the drum time to cool.
- Empty the lint screen, and see that the outdoor exhaust opening is free.
- If you smell gas at any moment, walk out and phone the gas utility from outside.
- Do not open panels or unplug the sensor.
- Call us to test the circuit and tell us if the room is damp.
How a technician diagnoses error code SH
- Confirm SH persists after a power cycle and the drum is genuinely cool.
- With power off and locked out, inspect the thermistor wiring for pinched or burned insulation.
- Check the connector for moisture, corrosion or bent pins.
- Measure the thermistor resistance and the resistance between its leads and ground.
- If the sensor passes, test the control input.
- Replace the sensor or harness that failed, then run a heat cycle.
- Testing a short means opening the cabinet near live wiring and gas parts.
- Telling a shorted sensor from a shorted wire needs meter readings of resistance to ground.
- A control that thinks the dryer is extremely hot is making a false decision, and only testing finds out why.
How error code SH differs from similar codes
SH is the shorted reading, while OP is the open circuit on the same thermistor.
Technical reference
- Document
- Tumble Dryers 120/170 lb Troubleshooting TMB1268C, Part No. 70399901R2, Dec 2016 (pp.53, 65)
- Maker documentation
- UniMac owner support
- Edition
- Part No. 70399901R2, December 2016; models through serial no. 0907000048
- Models / control
- Tumble dryers 120/170 lb (TMB1268C family) micro control
- Section
- Hybrid Timer Control Troubleshooting - 31. Error Codes, printed p. 53 (PDF p. 55); On Premise Micro Control (RM) Troubleshooting - 36. Error Codes, printed p. 65 (PDF p. 67)
- 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 UniMac dryer error codes
The drum is cool, so why does it say SH?
The control reads a shorted circuit as extreme heat. The display reflects the wiring, not the drum.
Can I unplug the sensor to reset it?
No. Leave panels closed. Unplugging it would turn a short into an open circuit and does not repair anything.
Will it clear on its own?
Not if the cause is damaged wiring or a failed sensor. It may only disappear for a while.
Need help with UniMac error code SH?
A technician confirms the cause on site and gives you the price in writing before any work starts.