These pumps are fairly basic. Not a whole lot of moving parts to go wrong as long as you use a decent prefilter - the impeller may need replacing from time to time, but that should be it. Unfortunately, I am now going on my FOURTH one in 8 years. To be fair, my house came with the first one, so I have no idea how old it was, but that one died within the first year of my ownership. I then bought a second one, which lasted for approximately 6 years. Not terrible, but disappointing that it only outlived the warranty by 20%. In June 2011, I bought a third one. Just over 10 months later, that one died. There is virtually no troubleshooting online, so I called Danner customer assistance. The woman I spoke with did not do any troubleshooting with me. She just told me to mail it back in and they would repair it because it is still under warranty. I told her about my previous ones, and she told me that 6 years was a good lifespan to get from one of these units, so it is not surprising. I then asked her how long it would take to get the repaired unit back (I have a pond full of koi that are dependent on a working filtration system). She told me that if I FedEx'd it in, they would turn it around as quickly as they could, but that it would be sent back out ground. Unfortunately, the cost to Fedex the unit was outrageous because of the weight, and it would still leave me without a pump for well over a week. Therefore, I ended up gritting my teeth and buying a FOURTH via Amazon Prime so I would get it this week yet and thus keep my fish alive. I will still send unit #3 in to get repaired as it is under warranty, but I will likely end up keeping it as a backup. After all, I pretty much expect the units to die just after warranty expiration. Very frustrating!

***UPDATE***  (8/26/14)
I am now on my FIFTH pump. They seem to die almost like clockwork every 12 months. I checked my purchase history on Amazon, and I have bought a new one every June for the past 4 years!  I suspect part of the problem is that there is not a good prefilter on the market for these units. The one that comes with it has to be cleaned out every week or so or else it gets clogged up and collapses on itself (even though it has a "rigid" brace in it to supposedly prevent that). All it takes is one prefilter fail and the pump dies, which is pretty unacceptable. I'm getting quite frustrated with it, but I have not been able to find any alternatives at this point.
These pumps are fairly basic. Not a whole lot of moving parts to go wrong as long as you use a decent prefilter - the impeller may need replacing from time to time, but that should be it. Unfortunately, I am now going on my FOURTH one in 8 years. To be fair, my house came with the first one, so I have no idea how old it was, but that one died within the first year of my ownership. I then bought a second one, which lasted for approximately 6 years. Not terrible, but disappointing that it only outlived the warranty by 20%. In June 2011, I bought a third one. Just over 10 months later, that one died. There is virtually no troubleshooting online, so I called Danner customer assistance. The woman I spoke with did not do any troubleshooting with me. She just told me to mail it back in and they would repair it because it is still under warranty. I told her about my previous ones, and she told me that 6 years was a good lifespan to get from one of these units, so it is not surprising. I then asked her how long it would take to get the repaired unit back (I have a pond full of koi that are dependent on a working filtration system). She told me that if I FedEx'd it in, they would turn it around as quickly as they could, but that it would be sent back out ground. Unfortunately, the cost to Fedex the unit was outrageous because of the weight, and it would still leave me without a pump for well over a week. Therefore, I ended up gritting my teeth and buying a FOURTH via Amazon Prime so I would get it this week yet and thus keep my fish alive. I will still send unit #3 in to get repaired as it is under warranty, but I will likely end up keeping it as a backup. After all, I pretty much expect the units to die just after warranty expiration. Very frustrating! ***UPDATE***  (8/26/14)
I am now on my FIFTH pump. They seem to die almost like clockwork every 12 months. I checked my purchase history on Amazon, and I have bought a new one every June for the past 4 years! I suspect part of the problem is that there is not a good prefilter on the market for these units. The one that comes with it has to be cleaned out every week or so or else it gets clogged up and collapses on itself (even though it has a "rigid" brace in it to supposedly prevent that). All it takes is one prefilter fail and the pump dies, which is pretty unacceptable. I'm getting quite frustrated with it, but I have not been able to find any alternatives at this point.