Dosing Pump Not Starting? What to Check When It Has Power
A dosing pump not starting is one of the most common service calls. Very often the pump is not broken at all. It has no supply, it is being held by an external stop signal, or the panel is set to wait for an external control signal. Sort out exactly what you are seeing first, then work through the checks in order, and you will save a lot of time.
This article uses the IWAKI EHN solenoid metering pump as the example. Other solenoid pumps follow much the same logic.
Three Kinds of Not Starting
Figure 1: IWAKI 易威奇 EHN-YN solenoid metering pump. Image source: IWAKI 易威奇 official website
- No response at all: the panel is dark and there is no sound. The problem is on the supply side.
- Panel lit but not running: the display looks normal, but pressing start gives no stroke. Usually a stop signal, external control mode or a panel setting.
- Starts, then stops: the pump strokes for a few seconds or minutes, then stops, often with an alarm. Usually a level switch, overload or a pump head problem.
Each points in a different direction, so observe carefully before touching anything.
Step 1: Supply Faults Behind a Pump Not Starting
Measure the voltage at the pump supply terminals and compare it with the nameplate. Check the breaker, fuse and contactor in the panel, and make sure any plug is fully seated. On a new installation, confirm the voltage rating as well; the wrong supply can destroy the control board. Wiring details are in IWAKI metering pump wiring.
Step 2: Check Stop and External Control Signals
The EHN has a stop input. When the external contact opens or closes, depending on configuration, the pump stops and the display shows a stop state. Two situations come up all the time. A level switch is wired to the stop terminal, so the pump stops itself whenever the tank runs low. Or the plant control system sends a stop signal that nobody on the floor knows about. Clearing a stop is covered in IWAKI pump stop release.
If the pump is set for external pulse or analog control, it does nothing until a signal arrives, which looks exactly like a pump not starting. Measure the control signal at the terminals, or switch temporarily to manual mode for a test run.
Step 3: Panel Settings That Cause Not Starting
A wrong setting can also leave the pump idle. Common examples: stroke rate set to zero or very low, the display left inside a setup menu, a key lock active, or the operating mode changed. Check mode and rate against the manual, and if needed restore factory settings and set the pump up again. See IWAKI EHN control panel settings.
Step 4: Read the Alarm Code
When the pump starts and quickly stops, the display usually shows an alarm. Codes point to overload, low level, external signal faults and more. Looking up the code is far faster than taking the pump apart. Common codes are listed in IWAKI pump error codes.
Step 5: Check the Pump Head and Mechanics
If supply, signals and settings are all fine and you hear the pump stroke but no chemical comes out, the problem is in the liquid end. That is a no-delivery fault, not a pump not starting. If the solenoid clicks but the pushrod does not move, or there is no stroke sound at all, the solenoid drive or control board may have failed, and the pump usually needs factory repair.
A Site Example of Not Starting
A wastewater station replaced an old pump with a new EHN. After wiring, the panel lit normally but pressing start gave no stroke, and the operators decided the new pump was faulty. On site, the display showed a stop state. The old level switch cable had been reused on the new pump's stop terminal, but the logic was reversed: the old pump stopped on a closed contact, while the new pump's factory setting stopped on an open contact. With the tank at normal level, the float contact was open, so the new pump sat in stop.
Changing the stop logic in the menu to stop on closed contact solved it immediately. Whenever you reuse old wiring on a replacement pump, check the signal logic of the new one.
Common Mistakes With a Pump Not Starting
Treating a Stop as a Fault
Many callouts end with the discovery that the level switch was doing its job. Once the tank is refilled, the pump restarts. That is normal protection, not a pump not starting because of a fault.
Bypassing Protection
Jumping out the level switch or removing the stop signal to force the pump to run lets it run dry on an empty tank and damages the diaphragm and valves. Find the cause of the stop and clear it properly.
Miswired Control Signals
A pulse signal wired to the analog input, reversed polarity, or signal cable run alongside power cable can all leave the pump without a valid signal. After any new installation or rewiring, check the terminals against the drawing.
Confirming the Fix
After the repair, run the pump in manual mode and confirm normal stroking and delivery, then switch back to external control and check that it starts and stops on the signal. Test the level switch for real by lifting and dropping the float. Check the control signal at its upper and lower limits so the pump does not cycle on and off near the edge. Finally, record the symptom, cause and fix in the equipment file, so the next case of a pump not starting can be matched quickly.
Conclusion
When a dosing pump is not starting, work through supply, stop and external signals, panel settings, alarm codes and finally the pump head. Most cases are solved in the first three steps. Never bypass level protection or stop signals to force the pump to run. For IWAKI and other solenoid pumps see our diaphragm metering pumps, or contact us for on-site help.
FAQ
Why is the pump not starting when the panel is lit?
Usually a stop signal is active or the pump is in external mode with no signal. Check the status display first.
Can I run the pump manually after a level alarm?
Refill the tank first. Running dry damages the diaphragm.
Should I replace the control board?
Only after ruling out supply, signals and settings.
How do I run manually while in external mode?
Switch to manual mode on the panel, then switch back after testing.
Why is the pump not starting after a power cut?
Check the auto-restart setting. Some models need a manual confirmation after power returns.