Heat get to radiator, but radiator stays cold

Hi, I am having a problem with one of my radiators (one pipe, steam system): the pipe to the radiator gets very hot, but the radiator itself stays cold.

I took off the vent off it and was able to blow air through it, so I think the vent is working. (If it makes a difference, this is the vent I have: https://www.homedepot.com/p/C-1-8-in-IPS-Angled-Steam-Radiator-Vent-Valve-A888/202246275).

The radiator is shimmed, but I don't know if it is properly pitched -- and I'm not sure how to measure the pitch.

Any suggestions?

Thanks!