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I'm an undergraduate aero-mechanical engineering student who lived in Malawi for 4 months last summer. I had issues with new (1-2 year old?) Grundfos borehole pump there but I was able to ultimately successfully resolve them with easy fixes; the pump is still presently operational.
Their local reseller wasn't that helpful and instead quoted us for a whole new pump assembly (extortionate and shipping from South Africa). We got it back up and running with a clean and some sunflower oil.
The pump we had was a highly sealed unit. The electronics and stator were one fully sealed stainless steel assembly, welded closed. The mechanical half was screwed on to this and was a shaft with permanent magnets and the pumping rotor (helical core). The mechanical half (top) was available more cheaply, separately from the electronics (bottom half).
The pump was made to fit in to a standard borehole, the type local contractors were familiar with drilling. Of course, the flowrate that the solar pump was capable of was an order of magnitude higher than manual pumps. This gave rise to some hydrogeologic issues - namely that the velocity of groundwater flow to this source was likely several orders of magnitude above that of natural groundwater flow,probably causing turbulent flow that was likely responsible for the pump becoming absolutely covered in wet, sandy mud/silt.
We filled up a tall tank of water and ran the pump for a while off some batteries, monitoring its performance. We really had to clean the internals of the mechanical parts though, some of the bearing surfaces were covered in this bizarre dry dust (dried mud?) that was somehow really clogging the whole thing up. The pump would start up for an instant but then decide not to bother within about 1s.
The grundfos pump had a water level sensor - believe it to be a pressure transducer - that required to be immersed water at some depth for around 5minutes before the pump wanted to start up. (When I initially brought the pump to them, the guys at the local Grundfos branch tried unsuccessfully to test run it by placing this sensor is a shallow plate of water....)
The pump used proprietary Grundfos "motor fluid" called SML-3, this floods the area between the rotor and stator in the top of the electrical half. Our pump didn't have any inside (very strange). This was not even available in South Africa, let alone Malawi. After some research, I believe the fluid to be antibacterial liquid with some antifreeze (and of course non-toxic). We substituted with sunflower cooking oil. Still working well. The pump was rated for 1.5kW but only connected to 350W of solar so we were pretty happy with the heat transfer there. We somewhat suspected the pump also had an oil sensor of some kind, which could've been another explanation for the aforementioned brief successful start up before it decided to turn off. It also had thermal protection which was very effective.
I would consider enquiring quite forcefully about warranty - Grundfos website says 2 years international warranty is included as standard.
They are very very well designed and engineered pumps that seem to protect themselves very carefully. This means they are hard to diagnose - it will protectively not turn on, rather than trying to power through internal mud/silt that might damage it. So units can look totally dead whilst actually in good condition.
Finally, dealing with the head office of Grundfos - their South Africa branch - was much, much more effective. They provided a required spare free of charge (we were able to pick it up in Johanessburg, by chance) and were very helpful all round.
I would be delighted to help further if able, send us a message on here if required.
Aero-Mechanical Engineering Undergraduate
University of Strathclyde, Glasgow