Does the boiler support an outdoor reset control? If it does, it will adjust the setpoint to the outside temperature and the return water temp automatically - making the water hotter as it gets colder outside and finding the return is cooling off too much.
What are the supply and return temperatures of the radiant loops? Depending on the type of floors and how the radiant pipes are installed, there is a limit on how hot you can make the water - you don't want to damage the flooring or have the beginning of the loop so hot you can't stand on it in bare feet! But, you may be able to increase it.