How would I drain possible airlock?

Hi @sjh , I'm thinking at least part of the reason for asking for a sketch is that it would be useful to get an idea where air might have risen to and be trapped in the system. Also, knowing where shut-off and purge valves are would make it clearer just how to move forward, using water pressure to flush out the air. Probably some mix of photos and sketch would do it. A sketch would just be to show how the pipes run and what valves or equipment is on them.

Yours, Larry

I thought this looked familiar. 

Here is the boiler that is in a separate room in the basement. There are two pipes from the boiler room that are labeled in this photo

Once those two pipes get to the other "Pump Room" that splits off into three other circulator zones. From the looks of things you have the PL 45 in the other pump room installed backwards.

The arrow on the PL45 is facing the wrong way

yes you could be air locked, so the new pump is not getting flow

Based on Ed’s drawing the pump is in backwards

It looks like you have valves to purge the 3 loops adequately

"The arrows on those B&G100s are pointing down, into the pipe the PL-45 is on. So I figured they're feeding it, not the other way around."

That would mean that two larger pumps are sending water to one smaller pump. To what end? You have 3 zones there. One thermostat for each pump. Each pump operates independently of the other pump.  If all three pumps pointed down, would that make more sense?

Here is the same picture with less 90° elbows. this photo has the other zones, C D and E

Zones A and B are in the boiler room. Without actually knowing the home's layout I believe you originally had two coal fired boilers in that basement and all those large pipes were connected to a lot of cast iron radiators that were heated by a gravity flow or thermosyphon design.

At some point somebody may have said that you don't need two boilers and that one boiler alone can heat the entire building. When the boiler that replaced those two coal boilers was installed with pumps all those big pipes could be fed with smaller pipes using circulator pumps. That is when the two boiler rooms became one boiler room and one pump room. 

Just photos of pipes without the context of the complete system, you will never get a proper answer to solve a problem.   Your statements will be understood as truth even if they are incorrect.  I was happy to remember this older discussion with all the photos that helped me to understand the boiler room(s) you have.   

Once you get the zone E pump installed correctly in the correct direction it may stop making the noise. Only time will tell.   

@sjh asked: "Is the PL-45 a zone pump, or is it boosting the other pumps?"

NO boosting. It is doing the same thing the other two pumps are doing. It is a zone pump

Maybe this will help.

This might be a coal boiler that could have been here a hundred years ago. There were no circulators on that old boiler because there may have been no electricity to operate them. Gravity or Thermosyphon technology was used to move the hotter lighter water in the boiler to the top of the system thru the supply pipes, and the colder heavier water in the radiators would go down to the boiler thru the return pipe. Those other two zone circulators were not there back then. Those pipes were connected to the ones that are capped off from that original flanged manifold.

Look closely at the flange at the top and the flange at the bottom. One is the supply and the arrow you have on that pipe is correct. The flange at the bottom is the return so you need to put an arrow on that pipe pointing in the other direction of the pipe on the top flange.

@sjh Said: "I can see what you're saying about a former coal boiler in that space. I guess the capped-off pipe I have circled in green was connected to it? And the pipes the B&G100s are on weren't there?"

You are correct. the B&G 100 pipes were not there when the coal boiler was there. The pipes that are capped on the cast iron manifolds may have been connected to those pipes somewhere else before the pumps were added.

The fact that there are 2 capped off pipes on each CI manifold and there are two circulators is a good indiction that the radiators connected to the B&G 100 pumps were at some time in the past connected to the capped off pipes on the CI manifolds. But that is only a guess based on 40+ years of experience.

You can see how the PL-45 pump is a zone pipe now, Right?

Booster is a term that was used by B&G over 75 years ago to sell pumps. It is like saying Jello™ even of your open a package of Royal Gelatin® and add it to the boiling water. You need to remember that over 100 years ago there were no pumps at all. Thrush was the first major pump supplier for the boiler industry. Bell & Gossett needed to tell the plumbers and pipe fitters of the time that their pump was better. You don't need a big pump. All you need is one of our "boosters" to get the job done. That way they sell more pumps than the other guy.

Remember you don't really need a pump back 100 years ago, so how do you get a boiler installer to add a pump. Call it something else and tell them you can use smaller diameter, less expensive pipes to get the heat where you need it.

So get the word "Booster" out of you head. It is an obsolete term and does not mean what you think it means in todays terminology. It is like saying this is a deluxe pump or a special pump or a space age pump, or a red pump. Even if you paint it purple or pink and you still call it a red pump. It does not make the pump any different. The name just sells more pumps.

The biggest thermostat manufacturer in the world lost a big market when the "think tank heads" at Honeywell called the software in their new thermostat "Intelligent recovery". Soon after the NEST thermostat became more popular because it was a "learning thermostat". Same idea inside the thermostat programing, just a different name makes one sell more thermostats than the other.

I better stop babbling on about trade names before I get too carried away.