new radiator wont come on

[young plum]

I have just had a new radiator fitted turned it on and nothing happens its not trapped air as i have bled twice but just wont go hot i am wondering if it has anything to do with little thing on bottom right with white cap as this is closed..... should it be open and what is it for

thanks

 

[bathjobby]

Assuming your not 'having a laugh', are you refereing to the return valve ?
You will get water into the rad by opening the feed valve, but you won't get any flow through it until you open the return valve too.

 

[oilman]

It's probably one of the new, intelligent radiators, and realising it's summer, it knows it doesn't need to come on.