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Bleeding Radiators in a Diverter Tee boiler with negative pressure?

3479 Views 12 Replies 4 Participants Last post by  Ocelaris
So we just purchased a new house about a month ago in Northern New Jersey and I've been meaning to ask around about this boiler system because it's unlike the one we used to have in our old home with baseboard heaters. The problem is that one cast iron radiator is cold, and the rest of the radiators are fine. Normally I would open the bleeder valve (with the system on) and air would pour out and then hot water would follow. But on the radiator with a problem it actually sucks air in! Actually it seems like most of the radiators have a negative pressure!

A little background on the system it's an original Bryant gas furnace which pipes a 1 1/4" pipe loop around the entire house (one floor rambler + Basement). It has what I think is a Dirverter Tee valve for take offs for each of the radiators, which is what I'm confused about how that works. But it's a continuous loop, i.e. the large diameter pipe never stops.

So my question is how do I "bleed" the system of air, I tried sucking a little air out of the radiators with a venturi pump (didn't really do much), and that seemed to get a little warmth into the radiator bottom section. I was thinking of getting a vacuum pump like you use to bleed brakes, Not sure if that'll produce enough pressure though.

So all the radiators basically are in Parallel and the pump is mostly just forcing pressure through the large loop it seems. I couldn't find a way to bleed the main system like I am used to with my old baseboard (copper tube with aluminum fins) which had 3 seperate loops for each floor, and bleeding the air out of the system by the boiler usually fixed any issues.

I'd like to look at replacing this boiler in the near future, but I wanted to get a high efficiency condensing boiler, but with this configuration of the radiators all in "parallel" with a continuous large loop, it seems I may not get the temperature differential I need to take full advantage of the condensing efficiency?

Thanks for any help, I can grab some pictures if it's confusing. Hopefully this diagram helps.
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Make sure your water supply valve is open to feed the boiler.
Turn off the power so the pump is off.
Now try bleeding that rad.

What is the psi reading on the tridicator when the boiler is off?
Thanks, I'll give that a shot when I get home. I would have thought that the system should be pressurized to bleed the radiators, but I will try turning it off bleed. The recirculating taco pump is very small compared to what I was used to seeing in our old house, but I assume (maybe incorrectly) that since it's been working fine for 50 some years it's not a design issue.

I didn't see any tridicator from the outside of the boiler, but I'll take another look tonight when I get home. I still have not found the flush/drain port on the boiler, but there is a 3/4" garden hose sitting next to the boiler, so I assume there is one somewhere. Thanks
Just to clarify. You may have had the gate valve that feeds water to your boiler turned off. Your water pressure may then have lowered over time to where it's barely enough to allow full circulation and not enough to exhaust the excess air out the rad bleed valves. In fact it can get to a point where when one opens the air bleed valves, air gets sucked into the rads instead of being exhausted.
Thats why I was looking for a psi reading of 15.
The pump gives the water it's flow but doesn't provide much water pressure.
Your boiler water pressure mostly comes from your house water pressure which gets reduced after the boiler gate valve by a reducing valve for the lower needs of the boiler.
After you bleed those rads, and before you turn your boiler back on. Drain your expansion tank. Then refill the boiler to normal pressure.
I just got home and my friend pointed out the fast fill valve.

On how's recommendation I flipped the fill valve to "fast fill" not "auto" (which it was on), and sure enough, water surged into the system and then I was able to bleed the radiators. I'm not sure why when it was on "auto" it didn't top it off.

I'm going to go back and drain the expansion tank, but do I have to wait for the temperature of the water to drop before I refill it? Thanks again for the help.
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No, you don't need to wait to refill. You may want to shut off the manual valve after your done refilling. That auto feed isn't reliable to fill or shut off from filling anymore. You don't want to over fill and have a big mess.
So I can't find a drain valve on the expansion tank, it seems to just have a 1/2" npt and the air fill valve. Can I just check the air pressure and equalize it to the house's pressure (or whatever the pressure reducing valve is set at?) I'm back to the problem where I can't see any drain connections on the system, except for a relief system which goes outside. So even if I disconnected the expansion tank, I don't see anywhere to drain the system. I'll go take some pictures.
If you have a bladder tank, it needs to be removed for the system pressure to check it. Good chance its ok though, and doesn't need checked, or more air added.

post the pics anyway though.
Thanks again for all the help. I found the tridicator and it's at 15PSI and ~130* Farenheit, so could I set the air bladder to 15 PSI?

I still don't see any way to drain the boiler, which I'm going to have to do when we redo the bathroom and move a radiator, so maybe there's one I'm missing?

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The water flow is reverse of what you have marked for the heating pipes.

Check the back of the boiler for a drain, or in one of the side panels.
Cold return watwer in on the bottom of boiler and hot water out the top of boiler.I don't see a system air vent near boiler.There should be a square keyed air vent at each radiator.You need a square key to open the little valve to let the air out.The 1 1/4 supply is plenty big enough for whole house.If you really have diverter valves then on the inside of those tees,there is molded in an actual blade the scoops water and forces uit into feeder leg going to radiator.
When you do get a new boiler make sure to get a Spiro therm air vent .There is simply no better air elimination valve on the market.There are plenty of immatators but none work as good.You should also have shut off flanges at the circulator.You don't want to drain the whole system if a circulator goes out.There should be shut off valves on either side of anything that might go bad.There is nothing I hated doing in the middle of the night then charge a lot of overtime to drain and refill and bleed a boiler.It makes no sense to have to do that when having valves would allow me to isolate the problem and fix it without all the hours it takes to drain it and refill it.The reason most boilers are not valved like tghey should be is because valves cost money and when a contrator quotes you he leaves them out so his quote is less.A casr of penny wise and dollar foolish.
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Thanks, I was able to bleed the system once I got the pressure/water level up. I'm still getting a handle on the whole layout, and it's probably been mostly untouched since 1953, I'm sure it could be much improved. I'll have to poke around more, but hopefully anyone else with similar issues will pick something up from the pics and discussion. Happy New Year! :jester:
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