3 routers all issue with 2.4Ghz, running out of ideas.

[#1]

Two weeks ago my year old TP-link router started dropping the 2.4Ghz signal and the replacement did the same almost straight away. I now have a Asus n56u which has kept the signal showing to all devices but has not allowed anything to connect to it.
I have the latest firmware in all devices. I has set the 2.4Ghz signal to channel 6 and have moved the channel extension to above rather than below.
IS there a common everyday object in a house that could be playing havoc with my 2.4Ghz signals. Getting pretty fed up with the hassle. At all times the 5Ghz and the wired Ethernet stay unaffected.

podman

[#2]

could be anything, microwave, bluetooth, some dect phones, baby monitor, video senders are the ones I can think of

[#3]

I checked the microwave is not on when it happens, bluetooth has never really affected anything before but is all off now. Dect phones are now away from all devices.
Will keep an eye on things and try and work out what it may be.
podman