Your radiator could be working properly, but the controls are screwed up. There are a lot of hot water systems like yours that operate on a "reset" schedule. What that means is that the radiator water temperature is set based on outdoor temperature on an inverse scale. So if it's 55 degrees outside, the radiator might get 120 degree water and feel warm. As the outdoor temperature drops, the radiator water temperature is raised. So it might not get to full temperature until it's 30 degrees outside.

This is done to save energy. Without the reset controller, the water is kept at the highest setting and tenants have to open windows to cool off on a warm winter day. That's obviously a huge waste of energy. But if you're not able to get your space to a liveable temperature, then adjustments can be made.