UniMac Washer-Extractor Error Code Eio 42: Door Lock Input Pin
Eio 42 is a hardware code from the input and output board for the door lock input pin. The board cannot confirm whether the door is locked, so the control stops the cycle for safety. Never bypass the door switch; power down and call us.
Medium: the cycle stops because the lock state cannot be confirmed, but the cause is often a switch or wire.
- Code
- Eio 42
- 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 42 mean?
Where the earlier lock codes concern how the board drives the lock, Eio 42 concerns how it reads the lock. On a UniMac QN washer-extractor, a pin on the input and output board reads whether the door is locked. The control needs that answer before it lets the drum turn. When the pin fails its check, the board cannot confirm the lock state, so the control stops the cycle for safety. The code stays until the board and the switch feeding it have been checked. The manual lists the door lock input wiring, the lock switch contacts, the I/O board input circuit, and replacement of the board only if testing calls for it. A worn switch or a wire that is intermittent is as likely as a failed board, which is why we test before replacing. The temptation to jumper or bypass the door switch must be resisted, because that removes the one check that keeps the drum from spinning with the door open.
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 42 is the door lock input check, separate from the lock output codes.
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 42 on the display and the cycle stopped
- Door that is closed but the control does not recognize it
- Intermittent stops that clear after reopening the door
- Code returning on the same cycle step
Possible causes
Listed in UniMac's documentation
- Door lock input wiring
- Lock switch contacts
- I/O board input circuit
- Replacement of the board, only if testing calls for it
Other likely causes — what usually sits behind error code Eio 42 on this control. A technician confirms which one it is before any part is replaced.
- A lock switch whose contacts are worn or contaminated and read open at random
- A door that closes slightly out of line so the switch only sometimes closes
- A connector at the switch with a broken wire inside the insulation
Safe checks before calling for service
- Write down Eio 42 and the door's behavior.
- Power the washer down, then wait until the drum is still.
- Never bypass the door switch.
- Call us to test the input circuit, keep the area clear and tag the washer out of service.
How a technician diagnoses error code Eio 42
- Read the code and observe how the door closes and latches.
- With power locked out, inspect the switch, connector and wiring for wear and breaks.
- Meter the switch contacts closed and open for continuity.
- Check the board input at the pin with the proper procedure.
- Replace the switch or wiring first when it fails, and the board only if it still reads wrong.
- The door switch is an interlock, and testing it incorrectly or bridging it can expose a spinning drum.
- Input readings are taken with the control energized near mains-powered circuits.
- Telling a worn switch from a board input problem needs a meter and the maker's test.
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
Can I bypass the door switch to finish a load?
No. It is the check that stops the drum with the door open, and bypassing it is dangerous.
Is it the same as Eio 30?
No. Eio 30 is about driving the lock. Eio 42 is about reading its state.
Does it need a new board?
Only if testing shows the board input is bad. A worn switch or wire is common.
Need help with UniMac error code Eio 42?
A technician confirms the cause on site and gives you the price in writing before any work starts.