i have just installed the main Router to the modem (virgin) and the connected the other two to the main one with patch cables on thw deak and they are working fine, i have then move the main to a different location with a longer eithernet cable back to the modem and the main is working fine.

i have then moved one of the Deco's to a different position with  cat 5 cable which id about 20mtrs long and the Deco is now not finding the Main.

its the cable i hear you say......no, i have put a cable tester on it and it is working fine.

please help me