I have a problem not so now but will in the winter, I recently installed new radiators up stairs as there were not any when I moved in, when I turned on the heating all of them worked but found a leak down stairs as I changed all the thermostats i then had to turn off the heating & water supply take the thermostate off the radiator and resealed it then turned on the water and heating now all of them work except one down stairs in the hall way what could be causing this? can anyone help