As Ploughman indicates, a breather switch isn't designed to prevent track buckles during hot weather. They are designed for transitions between CWR and jointed track, and are particularly found at the mouths of tunnels where temperatures are often very different in close proximity (very cold in the tunnel, warmer outside).
Stressing of the rails is designed to prevent track buckling, essentially making the rails behave as if it's 27 degrees all the time. When people say "how do the Americans and Spanish etc manage in hot weather? They don't have track buckles causing delays!", it's because they will stress their rails at a higher ambient temperature than we do, because they're average ambient temperatures are much higher all year round than ours.
It's also worth considering that the locations that have suffered from buckles in the last few days (or at least are at risk of suffering), may well have shoulder deficiencies. If the shoulders have deteriorated over the last few months and has not been correctly reinstated, the risk of buckling is much higher, hence all the TSRs going out.
