Thought you might appreciate a few thoughts on key issues in installing and maintaining a hot water circulator pump in such a way to increase its life expectancy and extend its period of trouble free operation.
Fluid Direction:

All pumps have a flow direction. Make sure you have the water going through the pump in the right direction.
Orientation:

Most of the pumps, or at least all the ones I have used must be installed with the motor shaft in the horizontal position. Read the fine print in the literature that comes with your circulator.
Location:

Do not install the pump at the lowest point in your system or the crud and sediment that accumulates there will shorten the life of your hot water circulator pump.
Cleanliness of Boiler Fluid:

Anything that might foul your boiler water will act as an abrasive to the internal workings of a traditional hot water circulator. Pumps have a moving impeller mounted on bearings for smooth and quiet operation.

Metal residues from boiler fabrication, rust, solder, chemicals and/or tape introduced during construction and lime scale developed during operation all contribute to bearing wear. If you get rid of the contaminants you get rid of the abrasive wear.