Reduce the room temperature thermostat to less than room temperature;- also deselect the radiators at the programmer. Open all the radiator thermostatic and isolator valves. Then bleed air/gas out of all the upstairs radiators-- the screw bleed core is at the top of each radiator, one end only.
When all upstairs radiators have been primed, bleed all the downstairs radiators. With all radiators bled, and bleed nipples closed, select radiator heat at the controller, and set the nearby wall-thermostat to 21C.