Air trapped in system

savage54

Hello I am new to this site, i was hoping somebody with more experience then myself could help me solve this problem. I have a 100,000 Weil McLain boiler feeding cast iron baseboard heating radiators. It is a one pipe system with mono-flo tees. The problem started when i removed the old steel expansion tank that was in the attic { causing ice dams on the roof }. So i installed a bladder expansion tank on the supply side of the boiler. Was told to move the pump to the supply side and add a unit call a sprial therm to remove all of the air in the system. The bladder tank is pre-charged to 18 psi., the boiler is operating at about 28 psi. when water temp is 170-180 degree F. All of my baseboards are hot. I have bleed all of the radiators, when i had line pressure [28 psi] flowing through the system with the pump off. Then turned the pump on and re-bleed the system { with little to no air coming out}. Allowed feed water to flow back throught prv to 15 psi. The house is a ranch, and the sprial therm is at the highest point in the system. When the boiler first starts it is quite, then with in 3 minutes it sounds like an old coffee pot perculating, then a slight bang. Then more bangs, as the water heats up the bangs get softer until they are very faint, then you can only hear them if you are standing next to the boiler. I have air bled this system about 5 times and its [ bang] is still their, so is the perculation. Help

Ironman

What's going on with the return and relief valve piping that's obscure in the pic? Can you post another pic that clearly shows that detail?

That looks like an Extrol 90 expansion tank. A 30 should have been large enough for a 100k but system unless there's an usually high volume of water in it. But I doubt that would cause your issue.

Is the cap on the auto vent on top of the boiler open? Cast iron boilers that have a separate tap out of the top like that for connection to a compression tank have an internal baffle or chamber to allow air to go up into a compression tank. If the auto vent is not open, you could be trapping some air in the top of the boiler.

Ironman

Also: if your fill valve is set to 15 psi, then the pressure on the bladder should be no higher than that. The way it is now, there will be no water acceptance into the expansion tank until the system pressure rises above 18 psi. Set the air pressure on the bladder with NO system pressure on the water side of it.

unclejohn

You should add another shut off valve at the boiler vertical riser before the supervent or spiral therm. Then when you fill the boiler shut the new valve and let water run out of the yellow boiler drain at the boiler. Connect a hose to that and drain it into a bucket until no air bubbles come out and your troubles will be over. And keep the pressure below 15psig. cold.

Gordy

I second @Ironman on what's going on with the pressure relief piping. From that pic I don't like what I see.........

savage54

savage54

Here is a pic of the prv piping

savage54

Ironman: would you suggest teeing in the 3/4'' tap on the top of the boiler to the 1 1/4'' copper supply line riser before the spiral therm air eliminater, and remove the 3/4'' bronze air eliminater on the top tap of the boiler?

savage54

Uncle John: Your saying to install a 1 1/4" valve in the copper riser before the sprial therm. Close the new valve and open the boiler drain valve {attached to a hose } i can put in a bucket. Open the water supply line valve to fill the boiler and piping system and when no more air bubbles show in the bucket the system is bled.

Ironman

savage54 said:

Ironman: would you suggest teeing in the 3/4'' tap on the top of the boiler to the 1 1/4'' copper supply line riser before the spiral therm air eliminater, and remove the 3/4'' bronze air eliminater on the top tap of the boiler?

It would be a lot easier to do the things I posted first.

savage54

Ironman :Ok will do, Thank you very much for your input.

unclejohn

The way the feed water enters the system it will flow into both the return and supply trapping air in the system. If you close your existing green handle valve when you fill you will force the water into the boiler out the return and you can putge through the boiler drain below the pump but you will still trap some air in boiler. If you force water into the supply and up through the boiler you will get more air out. One more very important thing is there a check valve in the pump?

savage54

I don't know if their is a check valve in the pump. Is their any identifying marks on the outside {body} of the pump? Enclosing some pics of the pump and a piping diagram of how spriotherm says to pipe the air eliminator in the system. Thanks for all your help.

Ironman

There's no check in that one - I think.

One thing that you've done differently than the diagram is placing the pump farther downstream from the spirovent than recommended. If it was in a horizontal or upward vertical flow arrangement, then it wouldn't matter. The way it is now, if an air bubble was lodged above the circ upon start up, it would have to pull the air downward against its natural buoyancy. It may not be the cause, but something to ponder.

savage54

Good point about the pump placement in the system. I will see what I can find out about a check valve in the pump. If it doesn't have one I will need to add one, and if that being the case I might move the pump closer to the spirovent and a check valve, because this air trapped in the system is getting really old.