Water works spa pump- need to remove wet end... through bolts are out, motor shaft is free, impeller is frozen in housing... impeller has no visible nut/bolt holding it on, is this press fit or other? how do I remove?

New pump wet ends have an impeller inside the housing and the impeller is threaded onto the shaft of the motor.
the four bolts go all the way through the motor and thread into the four little fingers on the wet end to hold it onto the motor.
Rod
US Parts Center

There are 4 bolts that go all the way through the motor and thread into the wet end.
The first place to start it to remove the face plate of the wet end exposing the impeller.
The impeller is threaded onto the shaft of the motor.
Take a big flat head screw driver and put it onto the end of the shaft of the motor and hold it tightly so you can unthread the impeller off the shaft of the motor.
Unthread those four bolts that go all the way through the motor.
You are done at this point.

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If you are asking how to replace shaft seal?

open & dismantle pump from motor. Some will have thru bolt motors all the way thru the motor, heads of bolts are (4 each) visible & accessible at back of motor. Loosen these & your wet end will be detached from the motor once the impeller is removed. To do this, block and prevent the shaft from spinning - normally there is access to the shaft which is located at center behind a cap at the back of the motor. Then unscrew the impeller from motors shaft.

It sounds like you have blown your shaft-seal. When this happens the pump runs dry. If you know that you have water but it will not pump, and all the cover and housing o-rings are good, it is the shaft seal. (unless the internal impeller is just broke, but this is unlikely)
Fix: Turn off power. Remove V-clamp holding wet end together. Remove diffuser inside wet end (need flathead screwdriver).
next remove rear electrical panel on the motor. Using s 7/16" wrend, hold the end of the motor shaft by the electrical end (where you removed the cover) while turning the impeller counter clockwise (note: some impellers have an impeller screw inside which unthreads CLOCKWISE) untill impeller is off. Replace carbon shaft seal inside. Reverse and prime and then restore power and start.

Take the screws off the outer cover fo the wet end. That will expose the impeller.
At the other end of the pump is a small metal cap in the middle. Pry that off with a screwdriver. That reveals the shaft of the motor which has a slot in it. This allows you to hold the shaft still with a large screwdriver.
While someone holds the shaft with a big screwdriver, you rotate the impeller counter clockwise to unscrew it off the motor shaft.
In my case the impeller was so caked onto the shaft with rust that we could not loosen it. We broke the impeller and still could not unscrew it. The screwdriver keeps jumping out of the slot in the shaft.
So the next step was to take the shaft out of the motor. On the far end of the motor are 4 small looking bolt heads. Undo those. They go right through the motor into the 4 legs of the wet end.
Stand the motor up with the wet end up. Pull hard to pull the wet end motor cover off the motor and you will then have the wet end and armature of the motor in your hands. Heavy.
Place some wood into a large vice and then grip the big silver part of the armature in the vice. Then unscrew the impeller.

You will need a 7/16 inch open ended wrench, a bearing puller, a phillips screwriver, a 12" peice of metal electrical conduit, and the bearings.
dismantle wet end of pump down to the impeller. Remove the shaft cap at the back of the motor(small circular cap in back). use 7/16" wrench to hold the shaft under the cap whiile spinning the impeller counter clockwise untill impeller is off. using a 1/4" hex driver remove the 4 through bolt located at the rear of the motor. seperate end caps on motor housing to access the bearings. use puller to remove. use the 3/4" conduit to tap new bearing into place. Reassemble unit.

Make sure you have an o-ring kit for this pump first

The front of the wet end must be removed to access the impeller. Then remove the rear electrical covering to expose the rear end of the motor shaft. Look closely at the shaft. It has two flat sides. A 12mm open face wrench will fit onto the shaft. Lock the shaft in place with the wrench and unscrew the impeller. The rear housing behind the impeller pops off to reveal four 9/16 bolts. Remove them and the motor is free. Reverse the process with the new motor.

First remove bolts holding motor to wet end. Pull motor back and out of wet end. Diffuser should just fall off. Not held by anything, there are just some locating tabs. Next, unscrew impeller. Some impellers may have a screw holding it on to center shaft. If so, unscrew.(Backwards thread). Remove back cover on motor and hold centershaft with large screwdriver or wrench on flat of shaft. Unscrew impeller. Next, unscrew 4 bolts holding motor to seal plate.

You will need to pull the front of the pump off then unscrew the impeller. The impeller will be set on the shaft and will take some force to break free. Hold ing the back of the shaft and using water pump pliers on the face of the impeller will usually work but sometimes I will wedge a screwdriver in the fin of the impeller and hit it sharply (not hard) with a hammer to break it free. Then the housing will just pull free of the motor. When replaceing, the impeller just goes on hand tight. Hope this helps and good luck.

You will need to remove the six bolts/nuts on the wet end to expose the impeller. At the rear of the motor, remove the cap covering the shaft and restrain the shaft and spin the impeller off (counter-clockwise). Check to see if there is a screw in the center of the impeller and remove it by turning clockwise (if applicable). Once the impeller is off, you can remove the four through bolts from the rear of the motor using a 5/16 nut driver and the wet end should come right off.