Coolant pump pump not working (PCNC 770) Troubleshooting suggestions?

The Mill sat mostly unused for a couple months from Nov-2023 to Jan-2024 and when I started using the mill again, the coolant pump doesnt turn on. The pump worked like a champ prior to that. Nothing changed regarding the set up. Nothing was moved around. This is the coolant pump that came with the tool. No aftermarket modifications. Here is what I’ve tried so far, and what I can answer:

I checked the plug going in to the mill, its plugged in properly.

I tried using both the physical switch on the Tormach, and the button in pathpilot, neither worked.

I made sure there is coolant in the reservoir.

There is no burning smell coming from anywhere.

The pump worked fine the last time it was used, there was nothing that happened then to cause issue.

I am not very good with electrical stuff, so I havent checked any wiring internally anywhere yet. I am not sure what else I can do to trouble shoot this. Can anyone offer up some suggestions of other things I can check? Hopefully there is something small I over looked.

MachineRobG - If you are inexperienced or don’t have a meter to test the outlet function, unplug the pump and use a known, good extension cord to see if it runs outside of the system.

If the coolant was in the tank, but still (not circulating), it can cause a calcification to build up on the pump shaft that will lock up the shaft.

Hope this helps


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Calcification was indeed the issue! Thank you for that tip! I’ll make sure to keep an eye on this from now on.

The pump on my 1100 did the same. Had to turn it by hand at first startup.
Have you considered using distilled water.
We ended up using deionized water for coolant in the plant. (steel can mfg) Before that coolant control, including biocide was a constant problem. Water chemistry is important to coolant life and effectiveness.


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We use a lot of DI water here where I work, so I will also start replacing the water with DI water as needed for the coolant! Thanks so much for this advise!

About to fill up my 440 coolant system for the first time (not in a 40hr/week production environment) so, hopefully I won’t have this issue…

Saunders has a good video on the subject.

Summary of what I’ve read/seen is that you should know (analyze/test) your water and that ideally you do want some amount of minerals/ions in it (but refills should be deionized). :man_shrugging: