What's wrong with this picture?

Can you talk about TRVs and one pipe steam? I have a bedroom room that bakes in the sun and freezes at night with a massive radiator in front of a bay window. When the boiler comes on in the morning the temp overshoots and we have to kick off the covers. I got a TRV for the air vent and it didn't seem to have much effect, so I got a remote sensor for it and mounted it to the wall by the air valve. Exterior wall by the window. No effect. Finally I moved the sensor to the end of the radiator by the steam pipe where it heats up first. Now it works pretty well and the covers stay on all night until we get up.

It sounds like your system is using a nighttime setback, which will not save on gas consumption, but merely cause temperature overshoot, which your TRV has been able to cope with.
Start a new thread for any future problems.
If this is an apartment building, check with management for:
1. The method of control-ie. thermostat, Heatimer control, etc.
2. The system pressure-lower is better, (under 1 psi). I heat 55 rads with a couple of ounces.—NBC

Wow. We seem to have at least two unrelated threads here, folks. @skyenglish and @LarryK , you'd both be much better off with separate threads.

First, though, @LarryK . A TRV (vent) on a one pipe system will do absolutely nothing to stop the heating on a radiator which has already started. It can only keep the radiator from heating -- or heating more -- if the boiler turns off and the pressure drops to zero at least briefly. In your situation, this isn't going to happen.

And @skyenglish -- I'm not sure whether you have a one pipe or a two pipe system; your mention of traps suggests a two pipe system. In which case, you need Thermostatic Regulator VALVES, not vents. Different beast. You also don't mention whether the boiler is correctly sized to the rest of the system (that's a pretty big boiler for a residence, but not unheard of). In any event, the system must be well balanced to begin with, particularly on two pipe systems with adequate main venting on the dry returns or on a one pipe system on the mains and then, the operating pressure must be kept reasonable (less than 1 1/2 pounds on one pipe and most two pipe, much less on some types of two pipe), and, on both systems the output from the radiators reasonably balanced to begin with (different vent sizes for one pipe, adjusting the input valves on two pipe). Only then can you think about using TRVs (vents for one pipe, valves for two) to adjust individual spaces for occasional desires (they can both lower the space temperature, neither can raise it) -- and only with great caution, as excessive use of them will result in the boiler short cycling very badly and wasing a lot of energy.