Intermitant fault in power head for electrolux z8420

Here's a YouTube video describing how to troubleshoot a electrolux 1590 power head. It will cover all possibly faults.

https://youtu.be/mQQ8HKByy3c

It is likely a wiring issue, check the continuity of the wires to the brush motor.

I have repaired many of these and to be honest your best course to to call Electrolux Home Care and find your nearest warranty station. The reason for this is it should cost you nothing and without the on ohm meter and a prior knowledge of how these are put together, you would not be in for a fun afternoon. Call them and explain the problem, most likely you have a broken or pinched wire in the neck assembly and will need a replacement. The wires to the neck attach directly to the main circuit board near the height adjustment, but to retain your warranty call Electrolux now... put down your mouse and call them so you can go back to enjoying your recent purchase with confidence.
(800) 896-9756 Monday-Friday, 9AM-8:30PM (EST)
Saturday-Sunday, 11AM-7:30PM (EST)

If it doesn't work after depressing the reset button, a wire in the power nozzle may have been knocked loose. If that's the case, it will need to be taken to an authorized Aerus Electrolux store for repair.

Lay the vacuum on it's front so you can see the bottom of the powerhead as shown below. Befrore going further, hold your hand straight and move your hand across the opening for the brush. If the bristles don't make good contact, the brush also needs replaced.
Remove the four screws. Using a flathead screwdriver, place it into the two rectangle openings (shown with red arrows) near the wheels and gently pry on tab to release the top of the power head.
Flip machine over and gently lift cover off and set aside.

This is what you should see. Remove the two screws at the ends of the brush. Check carefully how the ends of the brush fit in. Gently lift out brush. This is a good time to clean entire interior of the power head. Install new belt over motor shaft and teeth of brush: set brush into place. Insert screws. Check tension of the belt.
Replace cover of power head, being sure to settle front in just beneath the lip of the front of the base first. Press down until it "clicks" into place. Turn machine over and insert and tighten screws.
Your vacuum is now ready to use.

Start simplest always and work back to most difficult... so make sure you have power to the main unit, do you have a cheap voltmeter? If not they're cheap... Second check that connection plug is not stuffed with debris. Point is isolate whether it is the unit or attachment, most likely it's in the connection and repairable by you or used vacuum repair.

hi from uk may i suggest you try this ? recheck as you have done that although you have power to the switch ? you may not have the neutral wire feed back to the plug to complete the elec circuit have come across this problem many times and the cause /fault is most probably the neutral wire has broken within the actual lead where/just b4 it enters the hand lever on the upright this area issubject to excessive bending/pulling of wire also kinking if you have a test screwdriver ? and a switched plug? you can check the neutral wire is completing curcuit back to plug with screwdriver tothe neutral pin of plug if no live ?and switch is on ? then you can either find break in wire or renew the cable with longer length to reach further without having to change sockets ? hope this helps?

mine was the power head neck itself the handle got twisted to far and broke the wire a new neck cost 37 bucks online and i installed it myself wires get attached color to color and screw the head back together. it worked just like new!

S3765-040, power head would not run when the handle was elevated. Problem was with wiring from connecter plug on power head swivel into the power head itself, because of the design the wire tends to develop a short. Test it by turning on the vacuum, elevate the handle, then when it stops running move the visible part of the wiring with you foot/hand. If it starts/stops then you have a short. Replacement part was about $10.