Water – How to remove hot water baseboard

If the pipe is very hot going in and out of the baseboard then its probably not a problem with the boiler. You can try turning the water temperature up on the boiler. They normally go up to 200 but i would not go higher than 180 for efficiency. Every boiler is a little different on how to do this. Also if you have exposed pipes or radiators it should be lower to avoid burns

It is most likely something in that basement that changed letting in more cold air or its just being extra cold outside.

It is totally possible for thermal expansion to back some hot water into your regular cold water supply. A check valve will prevent this but you are correct in that this could cause an unwanted (potentially damaging) increase in pressure on the hot water side of the system.

You should look into installing a thermal expansion tank if this is enough of a problem for you as to consider installation of a check valve. It is a fairly simple and inexpensive solution; do an internet search and you will find a lot of information. Check with your local permitting authority to see if this is a DIY install, or call a licensed plumber.