Is a real simple thing to take apart and check the impeller is in good working order without cracks etc. The issues start when you try to put it back together!!
The pump has a backing plate, stainless steel and this floats until all three bolts are back in their respective mounts.
As you try to remount the pump housing the stainless steel plate moves about and this combined with the fact there are NO aligning pins for the housing means that you have to move the housing up/down and sideways to try to align the bolts with their appropriate bolt holes. This can be a long and arduous process if not careful as the stainless plate moves around blocking the bolts etc.
But there is a way to simplify and keep your sanity.
Align the impeller with the “key” on its shaft and then insert it into the housing, rather than try to push the housing over it on the shaft, making sure the impeller is as closely aligned when in the housing as possible. Put all three bolts through the housing and then the stainless steel plate onto this so that the impeller is now sandwiched between the stainless steel plate and the housing.
Then place a rubber band around the whole affair to keep the housing and plate together. This makes it a lot easier to place the housing on the pump without juggling all three parts.
You’ll need to wiggle the housing to get the impeller key to align as it goes on but if you have done a reasonable job of getting it aligned roughly it will not be hard.
Then you can get all three screw started in their threads. NOTE: this will take quite a bit of wiggling of the housing as it freely floats until all three bolts are in place and the impeller doesn’t because of the shaft, so you’ll need to compress one side of the impeller to get the threads to align.
Once you have all three started, you can cut the rubber band and pull it out and then continue to tighten the bolts down and you are done.