Electrical – Baseboard heater powered by a switch, not thermostat

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.

Sorry, the ONLY way to do this properly is to get the heater on a properly sized 240V circuit. This can be a 15A or 20A depending on what is shared on the circuit and what the distance is (less than a 150' or so circuit run this is not an issue).

If you don't want to do it right and find how the t-stat is wired you may be able to put an integral thermostat right on the unit and un-wire the wall t-stat. This depends on the age and brand of the heater if a t-stat is available for it. It's worth investigating thought. You may find the t-stat is wired right to the unit and has nothing to do with the receptacles.