It's only a side note, and I found now media reports about it, neither in German nor in English.
But airberlin posted on their Facebook site that due to a burst pipe in Terminal C the whole terminal had to close down today.
Terminal C is that "shack" used mainly by airberlin, but can indeed handle quite a lot of flights. Flights have been transferred to Terminal D. Terminal D is a little small terminal already too small for the few airlines they are handling now. It's not designed for transfer operations and I guess passengers had a lot of fun connecting between planes at this very little terminal.
While airberlin is the most affected airline by this they can't be blamed, however it's incredible why a burst pipe can close down a whole terminal these days. Tegel is doing very bad at the moment with all these flights that BER should handle today, there have been media reports the last days that Tegel can't handle all the bags and that lost bags in TXL are raising. I like TXL a lot but as we all know it urgently needs replacement and can't handle what they are handling today.