@User42 Sounds like replacing the leased router with a Deco would solve any number of your issues. You can expand the Deco mesh with up to 10 deco nodes. You may find that a 3node Deco M5 setup will...

@DaveinNE By the way, " My modem only has one Ethernet port", is a good thing. That forces any network connectivity, Ethernet or Wi-Fi, to be in the Deco network. That avoids the potential for...

@RobReid You didn't say what model the #1, #2, and #3 deco nodes were. Probably of no consequence, but...just in case. What Hardware version on the nodes and what firmware? Have you tried resetting...

@User42 Quite a bit more information will be required to give you any actionable suggestions. Which floor is the ISP Modem located? Is the ISP connecting via cable, fiber, copper DSL? I don't mean to...

@DaveinNE Yes the other Ethernet port on the Deco S4 will work to get your Dell on the network.

Yes to both questions. The Primary Deco Router determines what add-on functions are available.