I'm an Indian national. I'm travelling from Germany to India and I have a 9 hour stop at Heathrow Airport. I have to change terminals, does this mean I have to go through UK's Border Control?
No, you will not go through border control (unless you need to collect and recheck your luggage). I've done this many times and there are buses, airside, connecting the terminals in Heathrow. Just follow the 'Flight Connections' signage.
You will, however, go through a security screening at some point (in Terminal 4 if I recall correctly).