@Fred-  Hello, 

May I know did you buy a new KIT and the new KIT did the same as the old KIT?

Please factory reset your powerline unit by tpPLC Utility one by one :

https://www.tp-link.com/support/faq/1612/

tpPLC Utlity: https://static.tp-link.com/software/2021/202107/20210701/tpPLC%20utility.zip

Turn off Power save Mode on powerline units:  https://www.tp-link.com/support/faq/2018/

Later pair 2 powerline units: 

Note:  press Pair button only for 1 sec, Power Leds should be flashing on both powerline units in pairing process. ( if the Power Led does not blink, press it for 1 sec again)
When the Powerline Led or House Leds are on, the pairing process is done.

The one does not flash properly could be the faulty one. Can I know how does led flash when you try to pair them after factory reset? 

@Solla-topee Hi.

Thank you for your reply.

A couple of problems:

This link is broken: https://www.tp-link.com/support/faq/1612

And the Mac utility can't be installed because it's old.  It's from 2019 and Apple says it has to be updated.

I used the iOS (iPhone) app, but I don't see a way to turn off Power Save Mode.  How do I do this?

I reset the powerline unit both using the app and also on the unit itself with a pin. I then did the pairing

process and it seemed to work correctly, but when I relocated the powerline unit, it did not transmit internet.

Now when I try to pair the units, the Power LeD on the powerline unit blinks on and off about ever second but

the Home LED doesn't go on.  Also, the lowest LED stays on all the time.

Please tell me what to do.  Thank you.

@Solla-topee An update:

I downloaded the Windows utility and tried to do the Power Off, but it is not possible.  

Here's a screenshot of what I see in the utility when I click on Advanced:

@Fred- 

May I know the model number of AV600, like TL-PA/ TL-WPA on the back label. 

Make sure AV600 firmware are up-to-date: 

How to update the firmware using tpPLC Utility (new logo)?
https://www.tp-link.com/support/faq/1614/

For'  the lowest LED stays on all the time.' the bottom led should be the Ethernet Led, do you mean the Led is also ON even nothing is plugged into it? Is it the old wired unit/ old wireless unit? You could put aside this unit and pair other powerline units first. 

@Solla-topee 

The model number is: TL-WPA4220(EU) 

One unit is version 3.0, the other is version 5.0

I updated the firmware on both extenders.

When I try to pair the extender to the adaptor, the adaptor light blinks, but

on the extender the power LED stays lit and the WiFi LED is also on. The Powerline LED does not light.  

This is the same for the version 3.0 extender and also for the version 5.0 extender.

What should I do?

Thank you for your help.

@Fred-  Hello, 

The power Led should be flashing on the Extender as well in the pair process, if power led stays ON, you could press it again

• Try a different socket for it, press pair button multiple times
• Unplug it and plug it back in
• Try another factory reset : via the RESET button/ RESET hole

Press and hold the Reset button (or use a pin to press reset hole)  until most or all LEDs will turn off and start on again. (V3 reset for more than 5 secs, V5 reset for more than 2 secs) Could 42220 V3/ V5  be reset successfully?     

• Put adapter and extenders in another room and try to pair them
• If power Led falsh on both 4220s, you could also pair these 2 and see if House Leds are ON

Thank you for your time and patience with troubleshooting. 

@Solla-topee Hello!

Thank you for these latest suggestions. I reset both Extender units and then was able to pair them to the Adaptor by pressing the Pair

button on the bottom many times quickly.

I was also able to install both Extender units, in different locations in my house.  So now everything is working!

Thank you very much for your patience and continued assistance.  

Fred