The Wide Area Network (WAN) is for the connection to DCC, which would go over GPRS via the Telefonica WAN that runs alongside the O2 network. If you're able to get an O2 signal in the meter cupboard on just about any phone, that should be sufficient for a Smart Meter. The Home Area Network (HAN) however, is used for the local comms between the meters and IHD. As long as they're close enough to each other, they will connect. There's also new Dual-Band Comms Hubs coming out, which will resolve most HAN signal issues in places like blocks of flats.
I've hardly heard any reports of boilers not working after a Meter Exchange. However, if that has happened, it's probably due to unrelated matters and not because of Smart Meters. As for commissioning, the full process takes six weeks, but sometimes you can start getting usage data through much faster than that. My friend Blastoise186 literally managed to start getting data in just two weeks - and I've heard of a few cases where it was just 48 hours. Depends on circumstances really.
Just another guy passing by... The unknown tech way...
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