Hi,

I have a Johntech 0.55 kw borehole pump. When it runs dry the voltage increases rather than decreases. This indicates an overload condition.

I am using a M521 intelligent pump controller

Can anybody please confirm that this is normal or is the pump faulty?

Many Thanks

46 minutes ago, GarthW said:

When it runs dry the voltage increases rather than decreases.

I'm guessing the current drops, since its now pumping air and thus draws less power and thus the voltage of the source is able to rise... don't know your pump but what I wrote, is likely the case, so, nothing wrong with the pump, just the power source is not well regulated...

Thanks for the answer.

Sorry that was a typo, I meant amps not volts

1 hour ago, GarthW said:

Sorry that was a typo, I meant amps not volts

Ok, so if the current increase when running dry it could point to it running hot (no cooling due to no water flow) which would damage the pump/bearing, I'd assume, ideally you should have an automated mechanism in place that switches off the pump, once there is no more water to pump... hope it is not too far gone at this stage...

Edited October 20, 2025Oct 20 by Kalahari Meerkat
fat fingers...

2 hours ago, GarthW said:

I am using a M521 intelligent pump controller

Is this controller not faulty, is it not supposed to be intelligent and shut the pump down?

Thanks very much for your responses.

Yes the controller is shutting the pump off, but as an overload error and not a run dry condition.

The pump is running fine but it is still under warranty. I do not not want the pump to break, because of this condition, once the warranty expires.

11 minutes ago, GarthW said:

The pump is running fine but it is still under warranty. I do not not want the pump to break, because of this condition, once the warranty expires.

OK, well, it probably is a good idea to add in a flow switch or sensor, with which you can switch off the pump when there is no more water flowing, before it goes into heat/overload condition. Not sure how large your pipe is from the pump, if it is 1/2" then something like this could be used to switch a contactor, maybe, to drop the power to the pump...

16 hours ago, Kalahari Meerkat said:

flow switch

One would probably require a relay circuit with timed bypass to allow for startup. Instead one could also consider a phase angle relay on the supply to the pump.

I have the M521 controller but it has strange error, when the turning the pump on manually or pressing Auto the input voltage shoots from 233v to 285v. I dont think the pump even starts, the current reading on pump side remains 0.0. I then get an over voltage error. Any advice?

A bit late but here goes.

A couple of years ago a farmer friend had a borehole pump tripping mysteriously on overload. I connected a Owl current monitor and plotted the current on my laptop. What I found was that after about 19min the current started to spike violently as soon as the hole runs dry and that caused the pump to trip on overcurrent.

I think as soon as the pump sucks air, there isn't any new water to keep the column of water in the pipe above the pump, the pump speeds due to no load and then that column "falls" down on the pump, that then stops the pump from turning for a split second.

I installed a 8 event plug in timer to run the pump for 15 min on and 2h45 off, for the hole to fill again. This worked quite well and later when the level raised, he adjusted the timer for longer on and shorter hole filling time.

If you ever pull your pump, you can also make sure that the check valve at your pump outlet is still working and seals properly.

Hope you understand what I'm trying to explain.