Hello,

I have a house that has an oil furnace and baseboard heating. for some reason i keep getting air bubbles circulating through the baseboards. you can hear it and its annoying.

i've bled the system a few times, and after i do that it will be fine for a few weeks. but then the bubbles come back. there's no obvious leaks in the system as far as i can tell, where air can get pulled back in.

the system has a circulator pump at the bottom near the furnace. the zones are controlled by zone valves. i saw an episode of "This Old House" where they relocated a circulator pump to the hot side of the furnace, to PUSH heated water up to the baseboards in the upper levels of the house, instead of on the bottom, where it PULLS water down from the upstairs baseboards and pushes back into the furnace. they said that when it is set up to push water upstairs, it will keep the pressure on the system and not allow it to absorb air. they also said the air was coming from the expansion tank.

the system has an expansion tank on the hot side of the line (after the water gets heated and goes upstairs). should this put moved to the cold water supply line, before it enters the furnace?

should i move the circulator pump to the hot side of the furnace?

how can i get all the bubbles out and keep them from coming back?

thanks for any and all help!

 

Does the expansion tank have a air valve like a tire valve on it?

 

Yes, move the pump just past the expansion tank connection. The air is in the water as you are purging you are adding oxygen. When the water is heated the air comes out of solution and goes to the high points in the system. By moving the circulator you will add pressure to the system making the bubbles smaller and less buoyant so they can move down a vertical pipe. Once the air gets in the boiler and the boiler is firing the air starts leaving the water and gets removed in the air separator. Heat water and the air exits cool the water back down and the air enters.
By the way a circulator does not push or pull water. It only creates a pressure difference that causes the water to move. High pressure goes to low pressure. We want the water to absorbs the air in the system and get it back into the boiler and air separator, and maybe the expansion tank. Once the air is eliminated it will not come back providing the system is not drained, does not require a lot of make-up water or automatic air vents on the high points of the system.

 

Thanks for the replies guys!

To give more details, the system has one circulator pump and 3 zones, controlled by taco zone valves. I just look and i noticed that the expansion is installed on one of the legs of the zone heating. If it makes a difference the furnace is a Weilan Mclan (spelling?) The pressure gauge on the system says 32 psi, while the expansion tank says it is precharged to 12 psi. It is the design that has the bleeder/charging valve underneath it.

Everywhere i've looked on the internet says the expansion tank should be on the cold side of the furnace, between where it enters from the city, and the furnace. Could the air bubbles be caused by the placement of the expansion tank? Could changing the location of the expansion tank solve this problem?

thanks again!

 

Pictures ALWAYS help. The more the better. Pictures need to be uploaded to a photo hosting site and then the URLs posted here.

Are you SURE the pressure is reading 32 psi? Many gauges have dual scales and if this is true in your case you may have accidentally read the "altitude" scale. If it IS 32 psi then either the gauge is wrong or the safety valve is defective.

Yes, air bubbles in the system may be caused by incorrect placement of the expansion tank.

 

http://s294.photobucket.com/albums/m...=nav_tab_album

I just figured out how to use photobucket- pretty neat!

i took a bunch of pics and you'll see from them that the expansion tank is located on one of the legs of the three zones. should it be moved to the cold side of the furnace, i.e. inlet? should it go between the backflow preventer and the auto fill valve? or upstream of the backflow preventer?

will it be worth the effort of relocating the circ pump to the hot water side as mentioned before, and if so does it go shortly after the outlet of the furnace for the heating zones? (probably between the hot water outlet of the furnace, and where it T's off to make the three zones?)

the system also needs to have a tempering valve added. i just went to Home Depot, bought a 1/2 inch model only to realize i need a 3/4 inch finish

is the auto fill valve (valve just downstream of the backflow preventer) supposed to be left in the open position, or do i just open it whenever i need to purge the system?

and yes the T&P valve was dripping water, as you can see the amount by the bucket. which tells me the water is expanding in the furnace with no where to go but the T&P valve.

hope these pics help and again thanks again for all the help!

 

How much repiping do you want to do?

I would definitely change the position of that expansion tank. If it were my system I would create a manifold and purge station for the three return lines and then a single drop to the suction of the circulating pump. About half way between the manifold and the pump suction I would install a tee with a valve in the side connection for connection of the expansion tank.

This would cause the system to be "pumping away from the point of no pressure change" which is what you want.

I would also add a union in the drain from the safety valve to allow the easy removal of the safety valve. You should replace this valve if it has been leaking.

Leave the valve ahead of the backflow preventer open but leave the "fast fill lever" of the PRV in the released position.

 

I'd have a wye strainer with ball valves on either side right before your boiler.

 

Furd,

thanks for the detailed reply! yes sounds like i have lots of re piping to do. so what does a purge station consist of, i.e. what do i need to do to build this?

so the expansion tank doesnt need to go on the cold inlet leg?

is there any value in relocating the circ pump to the hot outlet side of the furnace instead of the return side?

thats a good idea about the union for the safety valve- the way its set up it has to be all cut and resoldered!

Who, what does the Y strainers do? and for the outlet side should it get added on the outlet to the drinking supply or the outlet to the heating system?

thanks again guys!!

 

The wye strainer keeps crud from circulating. It traps particals down to a certain size. Outside of that, not much to add from what furd said.

 

The expansion tank connection needs to be on the suction side of the circulating pump. It is sometimes helpful to have the pump on the discharge from the boiler but no matter where the pump is located it should ALWAYS be after the expansion tank connection.

Leaving the pump where it presently is and not changing any of the boiler discharge piping is just making your job easier.

The manifold and purge station is simple. You already have some purge valves (those hose bibs on the return piping) and all I am suggesting is to make a manifold out of tees and elbows to bring the purge valves to a convenient place.

Use black steel fittings, an elbow>nipple>tee (side pointing up)>nipple>tee (side pointing down)>nipple>elbow. Have the elbows pointing up so that you have three connection points up and one down. The down connection will go to the existing tee on the pump suction using a length of pipe and union that brings the manifold to about the middle of your chest.

Install nipples and ball valves on the three up-facing connections and then you can change to copper for the connections to the returns. Keep the copper tees with the hose bibs and install them (with sufficient clearance for operation) above the new ball valves. Connect the returns to the tees with the hose bibs.

The side of the tee at the pump suction where you remove the one return will now have a reducer installed to 1/2 inch pipe and a ball valve installed. Connect the expansion tank at this point. Ideally this ball valve should have a locking feature that holds the valve in the open position but you can use baling wire or a nylon wire tie. This valve is to be left open at all times unless you need to change the expansion tank.

 

Thanks for the tip about the manifold/tee system! I actually found on www.pexsupply.com that they make a cross fitting that will allow me to use a cross along with elbows to create the manifold you mentioned- so everything can be copper making it a little easier to work with!

i worked on the system a little bit tonight- i replaced the fast fill valve, the main valve into the furnace (was leaking), the air vent on top of the furnace, and also the pressure relief valve. also took the opportunity to remove the expansion tank, and check its pressure.

after the last time i wrote, the pressure relief valve had blew, and would not stop dripping. also noticed the pressure in the system was upwards of 28 psi- after replacing the auto fill valve and checking the pressure to the x. tank (was almost 20 psi, i dropped it down to 12) the pressure on the gauge to the furnace is now about 20 psi. also no leaking in the PRV. Does this sound like the system is now functioning correctly?

i have made about 10 trips to Lowes and Home Depot now and bought a ton of stuff i'll hopefully be able to return. i plan to add the isolation valves and drains, create the manifold system, and also relocate the expansion tank. also ordered a tempering valve, if it arrives by this weekend i'll add that too.

thanks again for all the replies!

 

I knew that a cross was available but I don't want you to pipe it that way for a reason.

If you use a cross you have a straight path for one zone return and double bend return for the other two zones. By using the tees as I suggested each zone has the same number of bends and while this MAY not make any difference it is the proper way to do the job.

I would also prefer that the manifold be made of steel fittings and connect to the existing steel piping going to the tee and on to the pump suction for the same reason of equalizing the friction losses from the three zones.

You can use all standard length threaded nipples for the interconnections.

The pressure in the expansion tank bladder when the tank is not connected to the system should be equal to the setting of the PRV/auto fill valve. This will also be the system pressure as read on the boiler pressure gauge when initially filled and cold. The pressure will rise when the system is hot and 20 psi is acceptable.