The regular summer pipe maintenance will deprive Muscovites of hot water on May, 14th this year, according to an announcement made at the city administration meeting. Buildings in Moscow receive hot water from a series of plants throughout the city, not from basement boilers. By summer, the plants and the network of pipelines that transport the hot water need maintenance. Some buildings, including hotels, install boilers, and some people put small water heaters in bathrooms.
The schedule of 2013 summer maintenance can be found here (russian): http://www.mos.ru/water/