The difference in temperature between the room and the water determines how much heat you can distribute along with the velocity of the water (i.e., the changeover). If you check the specs on the baseboard heaters, they will have values like x BTU/foot at 180-degree input. It will probably also be spec'ed at different input temps, and will also indicate the gallons/minute of flow. Measure the water temp - if you don't have a gauge, it wouldn't be a bad idea to put in two, one on the output and one on the return.
There could be a restriction somewhere (a valve not fully open maybe or a check valve stuck) that is preventing proper flow. Did they change the circulator?
If you search around on the net, you can locate a heat load calculator (spreadsheet, typically) that will tell you how much heat you really need to keep that area warm. If you have enough heat capacity in the heater, but can't get the rooms warm, then you may not be flowing it fast enough. There is a limit on how fast you can flow the water before you risk cavitation and wear on things. It is also possible that there is an air lock, and things just aren't circulating. Are there any air extraction devices in teh system? Did they purge the system properly? Is the pump the right size?