UniMac Washer-Extractor Error Code Eio 31: Lock Pulse Pin
Eio 31 means the input and output board found a hardware failure at the door lock solenoid pulse pin. The control ends the cycle and the load stays unwashed, so power down, keep the door alone and call us.
High: the board may be unable to engage the door lock, so the washer cannot run.
- Code
- Eio 31
- Maker
- UniMac
- Equipment
- Industrial laundry
- Applies to
- CHM1792C family washer-extractor (QN models, 20-100 lb) front-end control
What does UniMac error code Eio 31 mean?
To engage the door lock on a UniMac QN washer-extractor, the input and output board sends a short burst of current, called a pulse, to the lock solenoid. A dedicated pin on the board produces that pulse. Eio 31 means that pin failed its hardware check. If the pin fails, the board may be unable to engage the lock at all, so the control ends the cycle and holds the code, leaving the load unwashed. The washer will not run without a lock it can engage, because that would allow the door to open on a turning drum. The manual lists the I/O board connector at the lock output, the lock solenoid coil and wiring, the board's pulse circuit, and whether the I/O board needs replacing. The practical sign is often a door that does not latch when the cycle should start. It is not a problem with the door hinge or the load, so adjusting the door or load will not help.
Affected models and control systems
This applies to the CHM1792C family of UniMac QN washer-extractors, 20 to 100 lb, front-end control, for example the UCA020QN. Eio 31 is one of the door lock hardware checks.
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
- Eio 31 on the display before the wash starts
- Door that does not latch or does not click
- Cycle that never begins filling
- Load left dry and unwashed
Possible causes
Listed in UniMac's documentation
- I/O board connector at the lock output
- Lock solenoid coil and wiring
- The board's pulse circuit
- Whether the I/O board needs replacing
Other likely causes — what usually sits behind error code Eio 31 on this control. A technician confirms which one it is before any part is replaced.
- A lock solenoid whose coil has opened or shorted so the pulse never produces a latch
- A connector at the lock that has worked loose from door slamming
- A pulse stage on the board that has failed after repeated lock cycles
Safe checks before calling for service
- Note the code Eio 31 and whether the door would lock at all.
- Power the machine down and keep the cabinet shut.
- Do not try to hold or jam the door closed.
- Call us to test the lock circuit.
How a technician diagnoses error code Eio 31
- Read the code and check whether the door latch moves when commanded.
- With power locked out, inspect the lock wiring and connector at the solenoid.
- Measure the solenoid coil resistance.
- Check the board's pulse output at the lock connector with a meter in the proper procedure.
- Replace the lock solenoid or board once the failed part is identified.
- Pulse output tests involve live control voltage on the board.
- Latching a door by hand to start the cycle would defeat a safety interlock.
- Separating a failed solenoid from a failed board takes meter readings and the maker's specifications.
Technical reference
- Document
- Washer-Extractor Programming CHM1792C_SVG, Part No. F8641001ENR4, Error Codes Table 29 (pp. 100-107)
- Maker documentation
- UniMac owner support
- Edition
- Part No. F8641001ENR4, January 2020
- Models / control
- CHM1792C family washer-extractor (QN models, 20-100 lb) front-end control
- Section
- Error Codes, Table 29, pp. 100-108 (PDF pages equal printed pages)
- 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 industrial laundry error codes
Why is my load still dry?
The control never started the wash because it cannot engage the door lock.
Can I hold the door shut?
No. A door held by hand is not locked, and the control is right to refuse the cycle.
Is Eio 31 the same as Eio 36?
Eio 36 is the hardware check of the pulse circuit as a whole. Eio 31 is the pulse pin.
Need help with UniMac error code Eio 31?
A technician confirms the cause on site and gives you the price in writing before any work starts.