Then take an iron and set it to a medium heat.
How to get rugs to lay flat on carpet.
Double sided tape could be used in place of the carpet tape.
Turn over the rug with the right side down.
So the bottom line is that yes you can put an area rug over wall to wall carpet.
Many times this will allow the rug to lay smooth for a while.
Apply carpet tape around the edges of the rug.
Lay a damp towel over the edges and iron them flat.
Cut tape to fit each edge of the rug.
Apply the tape to the edges of rug.
Turn over the rug and lay it on the carpet.
However for rugs that are nowhere near furniture in the center of a hallway or foyer for example the carpet to carpet non slip pad is your best option for preventing ripples in your area rug.
If the ends still curl up move to the next steps.