Radiators not getting hot all over?
Use that small square shaped key and bleed the air out of the radiators (Hot water heat only) then make sure the automatic water feed to the boiler is working properly. If not have it replaced otherwise the radiators will not refill sufficiently. If your system has no circulator and has an open system, you will have to let water into the system manually. This valve is probably up stairs at the top of the system near the expansion tank, which has a gauge on the side to show how full it is. (It could be in the attic) If the tank is full, you will not have to add water. When you bleed the radiators the water in the tank will drop down to fill the gap left by the air you let out of the bleeder valves. Radiators that have covers that block too much circulation may also be the cause. Consider removing them temporarily and be sure to clean the mesh before you put them back in place. Just dust and cobwebs can restrict airflow.
If you have a hot air system and some rooms are too chilly, check to see if registers have been closed from when it may have been too warm. If they are open, check to see if the damper in the duct that goes to that register has been shut either fully or partially, that could also be the problem. Also, if you have furniture blocking the air ducts, move it until the cold weather passes.
Other sources of chilly rooms:
Storm windows not pulled down all the way from the bottom or the top. This goes for your primary wood or metal windows also. They should be closed tightly and locked. If you have replacement windows with no storm windows, it is especially important to make sure they are closed tightly from the top and the bottom and locked securely. If the house has settled, and you cannot close them properly, do the best you can and put caulking or tape over the gaps. You can address the problem when the weather warms up. The other obvious source of chilly rooms is the entry doors. They get a great deal of use and the weather stripping could have failed in some spots or the storm door might not be closing tightly.