@M_Larry Actual model numbers of the TP-Link products you are using would be helpful. eg. TL-PA4010, TL-WPA4220 V? Try plugging a computer into the ethernet port of the wifi powerline adapter (eg....

@Charlie2705 I don't own that particular product, but you should find the admin password and wifi passwords printed on small labels attached to each unit. You may wish to factory reset the units...

@FunsizePhil Yes you can install an unmanaged ethernet swtich between the router and master powerline adapter. fwiw, we have an unmanaged 8 port switch between our Sky Q hub and a TPlink AV500...

@Noab TL-PA4022P appear to be a pair of AV600 2 port pass through Powerline adapters. They do not offer wifi.

@lordlance You can install as many wireless access points as you wish provided their wifi do not interfere with each other. In a 'normal' network, there is just one 'router' which is used to connect...

@denyason If wifi signal is disappearing from the WPA-4220, check the hardware version. I bet you have v4 if you bought them recently? link to tplink forum If ethernet speeds to sockets on the 4220...