general comments
probably not in the least applicable in your problem but may not help
any radiator with a cover requires the thermostatic valve to be turned up perhaps 5 or 6 degrees to get a high enough amount off heat out to overcome the increased insulation off the cabinet along with the reduced airflow it causes
this can be further hindered by furniture or curtains
as soon as you said 3 story hot enough up stairs i off course thought open plan and hot air rises
do you have open plan or many doors open ???
try a close doors as you go regime to see what happens
this problem can often be exasibated by a " conservatory " open to the down stairs firing heat through the roof faster than a machine gun
probably not worth the time it took to write this post but thanks anyway “big all”.
thanks all for your comments guys I have a heating engineer coming to have a look today I will report back
