Iwaki Pump Stop Mode: Why an EHN Pump Stops and How to Release It

An Iwaki pump stop mode can come from four sources on an EHN pump: someone stopped it on the keypad, the external STOP contact is active, the pump is in EXT mode and receives no pulses, or an EHN-YN with an FCM flow checker has stopped on alarm. The external STOP contact is the most common, and it is usually wired to a level sensor in the chemical tank. The fix is to find which source holds the pump, then clear that cause. Pressing buttons at random will not help. This guide is for operators and electricians working on EHN-R and EHN-YN pumps. Exact display text, key combinations and terminal numbers are in the instruction manual supplied with the pump.

Four kinds of Iwaki pump stop mode

On site all of these get reported as "the pump has stopped", but each needs a different fix:

• Keypad stop: the pump was stopped by hand, or key lock is on and buttons seem dead.
• External STOP signal: a contact input stops the pump until the signal is released.
• EXT mode without pulses: the pump waits for pulses from a flow meter or controller.
• FCM alarm stop (EHN-YN): no suction flow detected, the pump runs at full speed for a set time, then stops.

Start by reading the display to see the operating mode and any alarm, then check whether a signal is present on the external wiring. Ask the previous shift whether anyone touched the keypad.

Keypad stop and key lock

In manual mode the keys start and stop the pump, and the stroke rate can be changed whether it is running or stopped. If someone simply stopped it, start it again from the keypad.

Key lock is the Iwaki pump stop mode that confuses people most, though strictly the pump is not stopped. After programming, the controller can be locked to prevent mistakes, and then no key seems to respond. Use the key lock release sequence in the manual rather than cycling power repeatedly.

External STOP: an Iwaki pump stop mode usually driven by level

Iwaki's catalog describes the STOP function this way: when the pump receives an external contact signal it stops, and it stays stopped until the signal is released. It allows ON/OFF control and pairs with a level sensor. The typical setup stops the pump when the tank level falls below the low limit, which protects against dry running.

So for this Iwaki pump stop mode, check the tank first:

1. If the level is low, refill. The signal clears and the pump resumes.
2. If the tank is full, check whether the float is stuck at the low position by crystallized chemical. Clean it and move it by hand to confirm it is free.
3. If the float is fine, check the cable for breaks or water ingress.

Isolate power before touching any wiring, and wear gloves and goggles when lifting the sensor out of the tank.

Input type and the ON/OFF setting

The STOP input accepts a voltage-free contact or an open collector. Do not apply voltage to it. The specification also notes that whether the pump stops on the signal can be switched ON/OFF in the controller settings. A classic trap: a normally closed level switch replaces a normally open one, the logic flips, and the pump stays in stop mode with a full tank. After any sensor change, check this setting.

EXT mode with no pulses looks like a stop

In EXT mode the EHN-R doses by pulse multiplication or division, so if the flow meter stops or the pulse wire is loose the pump stands still. The STOP input can also be reassigned from the keypad so that, in EXT mode, the pump runs in sync with the EXT signal when STOP is received. If someone changed this, the pump may look like it is in Iwaki pump stop mode when it is not, so include it in your checks. Full settings are covered in Iwaki EHN control panel settings.

FCM alarm stop on EHN-YN

With the FCM flow checker the EHN-YN offers three modes. In PA+AL mode, if the FCM sees no suction flow within the PA time, the pump runs at 360 spm for the AL time and then stops. In PA+AL+RE mode, once flow returns and continues for the RE time, the pump resumes at its set rate.

This Iwaki pump stop mode means a suction problem: empty tank, air in the suction line, or a blocked foot valve or strainer. Fix the cause, then reset as the manual describes. For air-bound heads see EHN not dosing and auto degassing.

Site checklist for any Iwaki pump stop mode

1. Read the display: manual or EXT, key lock, alarms.
2. Check tank level and the level switch.
3. Test the STOP input and confirm the ON/OFF setting.
4. In EXT mode, check the pulse source.
5. On EHN-YN, check FCM alarms and the suction line.

Never bridge or remove the STOP terminals as a permanent fix. The pump runs, but low-level protection is gone, and once the tank empties the diaphragm and valves suffer.

Conclusion

Clearing an Iwaki pump stop mode starts with finding its source. Restart from the keypad if it was stopped by hand, and release key lock by the manual. An external STOP usually means a low-level signal, so refill or free the float. In EXT mode, check the pulse source, and on EHN-YN fix the suction line before resetting an FCM alarm. Check the ON/OFF setting after changing sensors and never bridge the input. See the Iwaki EHN series, the Iwaki brand page and our solenoid dosing pumps, or contact us with photos of the display and wiring.

FAQ

The tank is full but the pump is still in Iwaki pump stop mode. Why?

Check for a stuck float, then check the stop signal ON/OFF setting, especially if the level switch was recently replaced.

Can I connect a 24 V signal to the STOP input?

Not directly. The input expects a voltage-free contact or open collector, so use an interposing relay.

Does an Iwaki pump stop mode erase my settings?

The catalog does not say it does, and the stroke rate can be set while stopped. Confirm memory behavior in the manual.

Will cycling power release an Iwaki pump stop mode?

No. If the external signal is still present, the pump stops again after restart.

Does the EHN-R have an FCM alarm stop?

No. The FCM function is on the EHN-YN. The EHN-R inputs are pulse and stop only.