First thing to ask is whether you have any devices connected to the SH2 by ethernet cables and if so what happens to them when the wifi connections drop out? If you dont know - can you test it? Its to ascertain whether the issue is just wifi related or an issue on the network connection - different solutions apply!
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John
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I do not work for VM. My services: HD TV on VIP (+ Sky Sports & Movies & BT sport), x3 V6 boxes (1 wired 2 WiFi,) SH2 in modem mode with Airport Extreme Router +2 Airport Express's. On VIVID200, Talk Anytime Phone, x2 Mobile SIM only iPhones.