Cold rooms in the back of the house

[Tricky-Dicky]

Had a similar problem at my house, as the downstairs warmed up the rising heat up the stairway hit the upstairs thermostat and turned off the upper heating. The solution was to re-site the upper thermostat. Moved it from the landing to the master bedroom, and the rad in this room is always set at maximum. Wired via the attic.
If I had to do it now I would install a wireless room stat, for ease. Bite the bullet. Regards