I recently inherited a job. The primary complaint is the cast iron baseboard are not all getting hot. The boiler is a dunkirk 150k btu, with domestic coil & 3 zones, circulators. The boiler is 2 years old, I don't know anything about the old boiler or if this was a problem with the old boiler also. The house is an average sized ranch. Main zone is cast iron baseboard monoflow. 1 1/4" supply splits to (2) 1" perimmiter supplys.
venturi tee is on the return side of the baseboard. On the opposite side of the basement, the supplies tee back to 1 1/4" and return down the center of the house. All air has been bled off . On a call for heat The burner and circ. start, the main seems to heat up in a reasonable time and the supplies to the baseboard are getting hot. The kitchen and 2 back bedrooms only 1/2 the base board gets hot, One section in the livingroom doesn't get hot at all. If the thermostat is raised 6 degrees, eventually all the baseboard is completely hot, but it takes 15-20 min for the water to make it through 10 feet of baseboard. There is a Taco 007 circ on this zone. There is 2 walls of baseboard in every room and a 6' length in the hallway. Today we moved the thermostat away from the hall baseboard. Other than a restriction in the pipes, I can't figure out why it takes so long for the water to move through the baseboard