A few questions about Hive, It looks like it consists of:-
1) a battery powered, Wi-Fi connected Room Thermostat
2) a Mains powered Wi-Fi receiver which replaces any existing Heating / Hot water controller and is connects to your boiler
3) a Hub (powered by a mains to DC supply) that is wired to your router and is also Wi-Fi
That's about the size of it. The internal communications are based on ZigBee, so a mesh wireless topology rather than what most people would understand by Wifi. The hub can only connect to the Internet via an Ethernet cable (and British Gas try to insist that it is plugged directly into the broadband router).
Q1) Does the system work (internally) without the Hub being connected to Hive servers via the internet?
Yes, it continues to operate fine if the Internet connection isn't there. The local devices can manage to turn things on and off to the schedule by themselves. The thermostat and receiver can also be installed without a hub. This is known as ‘stand-alone’ mode. In stand-alone mode the thermostat acts as a normal wireless thermostat.
Q2) Is remote control (outside your house) always via the Hive servers? rather than direct access to your router (with port forwarding)
Yes, it talks to the Hive servers - inside the house too.
I wouldn't really recommend Hive to anyone. I only got it because it was effectively free and I could install it myself, and at the time my ancient programmer in the garage was on the way out and although I'd sorted out heating control by installing a better thermostat inside and just leaving the heating on at the programmer, managing hot water was still a bit of a pain and boosting it involved going into the garage. Nest was fairly new and still only supported 24V systems.. I'm not even sure I'd choose it now - haven't looked for a while but I'm not sure about its ability to manage hot water.
Hive is missing some fairly fundamental features and British Gas even make Humax look responsive when it comes to updates. For example there's a way to boost hot water for an hour but the same option isn't there for heating and it can't turn the heating on early if it's particularly cold (most thermostats learn the time it takes to raise the temperature by a degree then can be told to get the house to 62 degrees by 7am for example - the feature is usually called something like smart start or optimisation).
The hardware is also fairly limited, not least by the thermostat having an LCD screen. On the user forums recently, BG said that the main problem they were having in implementing a heating boost (now 'in development' for 2 years) is that they need to make sure that it works even if the Internet connection goes down and they're trying to make the thermostat behave in a way that isn't confusing to users... so even if they implement heating boost I'm guessing the only way to work it would be through the app and when I'm in the house I want to use the buttons on the wall GDI!
All is not lost for me. There is an (undocumented and unsupported!) API that lets you talk to the BG control servers so I have written my own heating boost and smart start features. I have a job that runs each morning and checks the inside temperature and turns the heating on early if necessary. The heating boost will fail and leave the heating on if the Internet connection fails of course but I can live with that.
It's also apparently possible to hack the hub and get into it. Involves opening the case and soldering up a serial port but not too hard. I haven't got around to playing with that yet (search for hacking the alertme hub if interested). That might open more possibilities.
The Heatmiser kit may be worth a look (although I haven't researched it). I had one of their programmable stats for a while but sold it as the fahrenheit support was broken (displayed in fahrenheit but was still adjusting the temperature up and down by whole degrees centigrade) and it had the unfortunate problem of the screen backlight increasing the temperature reading. Build quality and looks were good though and another UK company!