Sounds like it could be a faulty Homehub. To rule out the Homehub 4 you could try connecting your Homehub 5 at your girlfriends house. If everything works OK you know you have faulty Homehub 4. If the fault is still there you wil know it is a faulty line.
hi i borrowed an old home hub 3 from a friend of mine, tried it at my partners house and it works perfectly now so it can only be a faulty hub 4. the reason i didnt take my hub 5 was that as i have Infinity fibre broadband and my partner only has the copper cable broadband, i was told by a BT engineer that neither the hubs NOR the filters were interchangeable (copper cable has ADSL filters, fibre optic has a phone socket with 2 outlets and filter is built in, i was told) but as it works perfectly with a hub3 i will be getting in contact with BT yet AGAIN (almost every day for almost 3 weeks now) to get the hub replaced as its a full brand new installation!
thanks for your help
HH5 is backward compatible to copper but HH4 is not forward compatible with fibre. Filters are exactly the same but obviously not required if faceplate filter fitted.
Glad you have established the fault. For your info the HH5 also works on ADSL just the same as the HH4. The HH4 also works on Infinity as long as it connects through an Openreach modem. The filters are also interchangeable.