Air???

STEVEN MARKS

Recently installed gravity hot water conversion system. Installer piped boiler with 1-1/4" pipe. Old gravity pipes were 2". Circulator (taco 007) is installed on supply pumping away from expansion tank. I responded to 2 service calls for no heat. Both times I found "air" trapped at the pump. With the pump and boiler off I opened the flow check. Air immediately traveled from the pump thru the supply piping and into the system. I vented all the radiators. No air found. System now functioning normal but with a high delta T.
I was thinking of installing a bigger pump Taco 0010.
Any thoughts?
Steven

Mike T., Swampeast MO

Are you certain this is a gravity conversion system? Unless there are two pairs of mains or the mains are quite short, 2" is rather small for gravity.

Best clues to original operation come from the piping. The lowest closest rads will usually be served by a pipe 1 size larger than a rad of similar size but further away from the boiler. Also, upper floor rads will usually be one pipe size smaller than a rad of similar size on the ground floor.

If it is in fact a gravity conversion, was the original open expansion tank (usually in the attic) replaced by a compression tank in the basement by the boiler? If not, it really should be.

If so, and an old, plain (no diaphragm) tank is in use is there a B&G Air-Trol fitting on the compression tank? (Rather odd looking red device with bleeder coming out the bottom at the tank connection.) If not, I'd really suggest installing one as air tends to migrate through the system after a fresh fill and the tank often winds up water-logged. The Air-Trol will prevent this from happening.

If there is an Air-Trol fitting, you fill the system by closing all air vents except the one on the Air-Trol. Then fill until you get a steady stream of just water from the Air-Trol vent. Then open the radiator air vents and close the Air-Trol vent. It's then a good idea to run the circulator continually for a few days and re-vent the rads. Then vent the rads once again after a month or so of normal operation. After this, and providing the system is tight, the air will stay where it should stay--in the upper half of the compression tank.

If modern bladder-type compression tank(s) make certain that the air side is probably charged (typically to 12 psi) and that the bladder does not leak! To check the charge on the air side of the tank you MUST remove pressure from the water side (if the installer was considerate, there will be a shut-off valve and bleeder in the line to the tank(s) just for this purpose).

Also, if this is a gravity conversion a Taco 007 is almost certainly sufficient given the pipe sizing. (It might even be a bit large if this is a small system.)