Radiators?

Try balancing the system. Radiators up stairs tend too get hotter than those downstairs or those nearer to the pump or boiler.
On one side of the radiator is a valve which governs the water input (turning it clockwise slows the flow) So, turn down those which get very hot and open those which are cold, tune the system. If one radiator is stubborn and is colder than the rest, turn off all the radiators and force the heat there, then keep cracking open the others until the system is balanced. Alternate, and turn off all the upstairs rads and so on. Bleed the radiators with the pump off. You will soon get it..

Bucket head
December 2010