Time between flights

Should be more than OK with the usual caution about your flight being on time.

You should be okay. Hopefully your flight to Germany is booked as a transfer on the same ticket as your flight from Boston to Heathrow.
If I was flying on a budget air carrier, I'd try to give myself more time than 2 hours to transfer terminals, etc. Don't showup for your scheduled flight on a budget carrier and you have to pay full value to get there.

Here is the official Heathrow website page with full details on transfers. You will need to put in your specific flight information (which terminals you will arrive and depart from, which in turn is determined by which airlines you are using). http://www.heathrowairport.com/heathrow-airport-guide/flight-connections/connection-guides