I replaced impeller and can't replace the housing cover

Depending on the pump you have to separate the motor from the housing bust removing the bolts. Once the expelled is exposed, remove the cover and the back end of the motor housing the electrical wiring. You can access the shaft of the motor and hold it in place with a small box wrench. Than spin the expelled off counter clockwise. Replace the melchanical seal and reinstall the impeller. Replace the seal for the housing and reinstall the housing to the motor. Fill the pump with water again and turn the lower back on

Replacing your pool pump motor
Gather the following items.
Phillips and flat head screwdrivers
Circuit tester
Dry towel
Step One
First, make sure that the power to the pump is turned OFF. This means turning off the breaker at the panel box and not just the switch at the pump.
Step Two - Removing the motor assembly
Remove the four hex head bolts which hold the motor assembly to the pump/strainer housing (These bolts may not be visible).
Slide the motor assembly out of the pump/strainer housing, exposing the diffuser. Pull the diffuser of of the seal plate, exposing the impeller. (The diffuser may remain in the pump/strainer housing. To remove, pull it straight out of the strainer housing.)
There will be a gasket or O-ring sealing between the motor mounting bracket and the strainer housing. Inspect this thoroughly and replace if necessary. An economical option would be to purchase a Go-Kit which includes the pump shaft seal and all necessary o-rings, gaskets and lubricant for your pump.
Step Three
Now, you can lift up the motor with bracket attached to get to the wiring more easily. There may be a bare copper ground wire attached to the outside of the motor that you will need to disconnect. Remove the cover plate on the back of the motor to get access to the wiring. You should have one green wire that is the ground wire and two other wires that are your leads. The lead wires should be black and white but could be any other color except green. Disconnect these wires (they may be attached to a screw, held down by a nut, or clipped on with a terminal clip).
Step Four
Next, you will need to disconnect the conduit (sleeve covering wires between motor and switch or junction box). This usually means unscrewing the compression nut that is screwed on the adaptor which is screwed to the motor. After unscrewing the conduit compression nut, you can pull out the wires from the motor. If you wish to reuse the adaptor, unscrew it from the motor.
Step Five
Now you must remove the impeller from the motor. Remove the volute covering the impeller if it is there. (Some are screwed on). You will need to go to the opposite end of the motor and pop off the plate covering the shaft. The shaft will either have a slot in it for a screw driver or is flattened to allow you to put an open end box wrench on it. This will allow you to unscrew the impeller. You will unscrew in the direction that is opposite to the direction that the veins point at the outside of the impeller. This is the same direction that the motor will rotate the impeller. This may look backwards but the water comes into the center of the impeller and rolls off the veins away from the impeller by centrifugal force. As you take the impeller off, be sure to note how the pump seal is positioned. We highly recommend replacing the pump seal with the purchase of a Go-Kit when replacing the motor.
Step Six
Now you can see the bolts that hold the motor mounting bracket to the motor. Unbolt these, separating the motor mounting bracket from the motor. You are ready to reverse the process to install the new motor.
Step Seven
Important Notes on Reassembly: DO NOT touch the ceramic faces of the seal; This may cause the seal to burn up and leak. Be sure to tighten the impeller completely. Be sure to wire the new motor for 110V or 220V depending on what you have. This may be a simple switch in the motor or you may need to use the wiring diagram on the motor to set for the proper voltage. (Black tracer means the white wire with a black line corkscrewing around it.) Be sure to put the volute back on, aligning properly. Be sure to reconnect the bare copper ground wire to the ground lug on the new motor. When tightening bolts, alternate tightening a few turns at a time to seat evenly or the pump may leak. Fill the strainer housing with water before starting the motor to prime system and prevent damage to seal and impeller.
More Helpful information on how to replace a pool motor
Shaft Seal installation
Clean and lubricate the impeller hub shaft and pump housing seal recess with a dilute solution of non-granulated liquid-type soap
Gently wipe the black, polished surface of the spring seal assembly with a clean, soft cotton cloth. Press the spring seal assembly onto the impeller hub with black polished surface facing away from impeller.
Gently wipe the polished face of the ceramic seat with a soft cotton cloth. Lubricate the O-ring on the ceramic seat and press it firmly and evenly into the recess of the seal plate with polished side facing out.
Place the seal plate onto the motor mounting bracket aligning the positioning lug and guide.
Replacing the impeller and diffuser
Slide the motor assembly, with the diffuser in place, into pump/strainer housing, being careful not to dislodge the diffuser.
Fasten assembly to housing using the four bolts. (Be sure housing gasket is in place.) Tighten alternately and evenly

Replace the water pump this is the sign its bearings are going out and they start leaking out a weep hole in the back

Compare old and new impellers, the new one must be bigger. Return it for the correct one.

Remove impeller housing cover. Insert screwdriver carefully into back of motor to keep the armature from turning then unscrew impeller clockwise or opposite the direction of operation. Replace seal on impeller and pump housing. Lube seal with graphite. Replace impeller and housing cover. Remove screwdriver from motor. You should be good to go.

Bearing have gone bad in the electric motor. You will have to replace the electric motor. They are expensive but still cheaper than buying a whole new heater.

how do I change the impeller on a barracuda 2595?

You will need to get access to the impeller, then unscrew it counter clockwise. You will have to hold the shaft of the motor to unscrew the impeller. You can gain access to the shaft by popping off a little round cover on the back of the motor, you should see a slot in the motor shaft. Once you get the impeller off, unscrew the thru-bolts. The housing should pull right off. From there you can pop out the seal half that is in the housing and replace it - the other half of the seal is on the impeller. These 2 pieces come with the new seal. When you put the housing seal half back in use some silicone around it. The impeller end just pushes on. Link to Aqua Flo XP2 Diagram

1. Shut the power off.
2. Disassemble the pump case by unscrewing the
bolts holding it.
3. Take the impeller (rotating element) off the shaft,
as well as the impeller cover (difuser) if there's
any.
4. Take off the mechanical seal taking care of the
ceramic seat, and the carbon ring. Should this
break, you have to replace it. Just leave the
ceramic seat in place.
5. Now, you can take the motor off from the pump
housing.
6. Now, you can mount the replacement A.O. Smith
electric motor to pump housing.
7. Remount the mechanical seal, the same position
when you take it off.
8. Then, remount the impeller, the difuser, and the
pump case cover. Take care of the O-ring serving
as gasket.
9. Once you reassembled the unit, reinstall it, prime
it up.
10. Put the power on, and start the pump. Okey.

I am not sure what you mean by impeller seal so here are a few scenarios:

**Note: Based on YZ250. others may be similar.

-If the gasket around the impeller housing is leaking you can replace that on its own. Open rad cap, drain the coolant using the lower screw with the copper washer behind it. Then remove the other 3 bolts, remove cover, clean mating surface, install new gasket, snug everything up, and replace the coolant.

You don't need to replace the head gaskets unless your leaking from there, or getting coolant in the engine.

The same would apply to your base gasket.

just in case:

-if your transmission/gear oil is milky, your will have to change the oil seals on the impeller shaft.