if you have an SSFP like this then yo d not need filters in any extension sockets - unless your wiring is incorrect and you have star wiring which need to be fixed
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This thread is two years old. At the time of writing the information was correct. BT now do "self install" for Infinty 1 and 2 which obviously means there is no engineer visit. If you do not have a filtered master socket you use the filters that BT supplied with the Homehub.