a few years ago we remodeled and installed baseboard heat on the second and third floor, third floor is fine, on its own zone,however the second floor went onto its own zone as well with 3 seperate loops, no problems first year. but this year one of the loops seems to be cold. could i possibly have some sort of airlock?, if so what would be my remidy..if im not using the correct terminology, by loops i mean my feedline tee's, then one of them tees again .all entering back into my return line. i have noticed though my pressure is running a bit low ,near 10 lbs. it seems to me when i installed the unit i ran it 15-18 lbs. any help would be appreciated and the kids will be warm in the cold vermont winter

We have an HB Smith, cast iron, oil fired, boiler in our home. This unit heats water to feed a radiant heating system in the ceilings of the house and the floors of the Florida room. The house heat is moderated by a four wire thermostat that drives a motor-driven valve sitting in the hot water line to the house. This valve modulates hot water flowing into the pipe / manifold headed from the boiler to the house ceilings. We also have a manual valve that controls how much cold water, returning from the house, mixes in with the hot from the boiler. We were told to use the manual valve to adjust the temperature of the outgoing water to 90 - 100 deg F. The motorized valve also drives a Taco SR501 that controls the circulator for the house. There are no zone valves inline with the "house" pipes. The Florida room has a different design. There is a manual valve that controls how much hot water from the boiler mixes with the cold water returning from the Florida room floor (no motorized valve). A ordinary, Honeywell hockey puck thermostat connects to a Taco 572 zone valve that controls hot water flow into the Florida room floor. Wires from the Taco zone valve connect back to an second SR501 that controls a separate circulator for the Florida room location. Hot water from the boiler circulates through an external coil / tank combo that heats hot, potable water for the house. An sensor in the tank, coupled to a third Taco SR501 and a Taco circulator controls the temperature of the potable hot water. Finally, a Honeywell L6081A 1010 aquastat and an R8184 Protectorelay controls the Beckett oil burner itself, switching same on when the boiler drops below a set point temperature, and switching it off when the desired temperature is reached. I have three questions: 1. Considering we're sending 90 - 100 deg F water through the radiant heating pipes, how hot should we run the boiler? Right now, the oil burner comes on at 140 degrees F, and turns off at 165. I assume that the hotter the temperature, the more heat we're wasting into the cellar air. Some boiler technicians are saying 180 / 200, while others are saying 140 / 160. Since the boiler is 60 years old, it's NOT insulated at all. 2. Are we better to have a wide swing (25 deg F) between On and Off temperatures, or small swing (10 deg F)? On one hand, less "on and off" cycling would provide less wear and tear on the mechanicals, but a smaller swing would keep the boiler at a more consistent temperature, causing less expansion and contraction with the metal. 3. Does anyone have a white paper on how a four wire thermostat and a Barber Colman motorized valve work together? Thanks for all of your help. There's no documentation on the system, and I'm trying to remedy that. Rog