I have concluded that my Deco X1500-4G has irrevocably failed, leaving my five Deco E4 satellites 'marooned'. I still have an ISP-supplied Huawei B310s 4G which works.  I have trawled through the many posts on this forum about connecting an E4 by to another modem, but have got totally confused (old age!).  For example, without an active Deco wifi, I can't use the Deco app to change any settings. Please can someone point me to a link that CLEARLY explains what to do (as I am not even sure whether it should work).