We did not have hot water for two days during a three-night stay in Berlin in December, with outside temperatures around –1°C.
When I reported the issue, the staff did not seem surprised or particularly concerned. No compensation was offered, and despite sending a message after our stay, I never received any response.
Technical issues can happen, but a minimum of empathy and a commercial gesture would have been appreciated. In my opinion, this hot water issue seems recurrent, so if you are sensitive to the cold, I would not recommend this hotel.