While setting up my 3 unit mesh I have encountered the following problem which makes the system unusable.

The main deco unit has a hard (ethernet) connection to the router and works fine.

Originally, one of the satellite units connected (green LED).  This was positioned in a different room to the main unit but on the same floor of the house.

The second satellite unit (positioned upstairs from the main unit) would not connect and showed a flashing red LED.

I brought the second satellite unit downstairs to try connecting it when it was next to the first (working) satellite unit.  It would not connect and showed a flashing red LED.

I switched off both satellite units while I did some research on what the problem might be and when I turned them on to try and connect to the main unit again, neither of them will connect to the main unit.  They both show a flashing red LED.

I'd appreciate any help in resolving this problem as if I can't fix it in the next day or so the units will be returned and I'll have to find something else :(

Many thanks