We've just moved into an 1930s block of flats with a central heating system. All rads are on full blast and cannot be turned down/off. The valves turn in both directions (on/off in theory) but the rads remain boiling at all times and the flat is unbearably hot. A bathroom installer has had a look and says that the rads simply cannot be turned off unless the whole system (80 flats) is drained -which we won't be allowed to do- and the individual rad valves replaced. Any ideas about what the exact problem may be and what we could do about it? Could the bottom part of the pipes be frozen and new valves fitted? Cheers.