Part of the radiator remains cold at the top
ANSWER:
The radiator probably needs to be vented.
My radiator remains cold even if it is vented and the room is cold
ANSWER:
Valves can be blocked. In long periods without use, e.g. from spring to autumn, material from the water can deposit on the valve pin causing it to stick.
In order to solve the problem the sensor must be removed from the valve. When the sensor has been removed from the valve, you gently push down the pin protruding from the valve (never pull!). The pin should be able to move 2-3 mm, otherwise it is stuck. In order to loosen a stuck pin you can try changing between gently beating the valve on the side and pushing down the pin until the pin again moves freely. When it is again moving freely, you re-mount the sensor.
If the above procedure is not successful, you should contact the heating technician.
The radiator under an opened window in my bedroom is warm even though the sensor is turned to minimum setting?
ANSWER:
The sensor is frost protected when turned to minimum setting "*", corresponding to approximately 5oC. Therefore if it is very cold outside, the radiator will continue to be warm in order to avoid frost damages to the system.