sounds to me with the little amount of info to work with that the system doesn't have enough pressure on it (approx 12 to 15 lbs)and is air bound. Add water to the system and then bleed out all the air in the baseboard or the rads.The other problem could very well be that the circulater isn't working. Test it for power. The third thing is to make sure is if you have a double or triple aquastat the is power going to the circ. side of the control. good luck.
Michael Mefrank4@hotmail.com, April 2006