Air in hot water system


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Old 12-22-17, 01:14 PM
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Air in hot water system

While remodeling a bathroom this summer, I replaced a short baseboard with a Runtal radiator. I filled the system and bled it, and initially it worked great aside from a faint trickling noise. However, that trickling noise grows louder day by day, until it reaches waterfall level and I bleed it again. That quiets it down for a few days, but then it gets loud again. Typically, when the pump first turns on, there is a brief loud air sucking noise from the Runtal, then the trickling sound.

So, clearly air is getting into the system. The questions are how is it getting in, and how to prevent it. There are no obvious leaks (I don't see water leaking out anywhere that is accessible). I figure there is a problem with how I am venting the system. The Runtal is in series with a long baseboard (the only other radiator in this zone). If I vent the Runtal cold or hot without the pump running, I get water coming out of the vent but no air. If I open the vent and then start the pump, a burst of air comes out. Then, water comes out with a few air sputters, and often a fairly large air bubble makes its way out as the radiator gets hot.

This heating zone is on the second floor, and the boiler is in the basement. The two other zones have not developed air or noise problems. I attached a diagram of the system. The zone with the problem is zone 3. Note that this is the only zone with a spirovent. The expansion tank is not a diaphragm tank, but a plain old tank mounted a couple of feet above the boiler. It does have water in it, and it doesn't seem to be full.

Where could the air be coming from, and what is the correct way to bleed zone 3?

Thanks in advance, and happy holidays to all!

(Diagram: Red = pipes, blue = devices, black arrows are direction of water flow)

(Edited to add: as far as I can tell, the pressure is correct - 12-15 PSI according to the indicator on the boiler. The temperature seems correct as well, but I haven't measured it. The Runtal is first in the series and gets very hot. The baseboard doesn't get as hot, but the system heats the rooms very nicely even with water gurgling.)
 
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Old 12-22-17, 01:49 PM
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S,
What is your system pressure when bleeding your system.

Unless you are raising your pressure to about 25psi to bleed so when you are done bleeding the auto feeder doesn't
let fresh water you might be getting air from the fresh water entering as you're bleeding.

Do you have manual or auto vents on the system. If an automatic vent is installed sometimes when a pump comes it will suck air into the system so will never see a water leak but you can have an air problem.

You should always bleed your system with the pump off using the boiler pressure and not the added force created from the pump.

Hope this helps a little.
 
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Old 12-22-17, 02:18 PM
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Thanks for your response. As far as I can tell there are no auto vents - but I'm sure what they would look like. Can you describe what I should look for? (There is a spirovent - not sure if that's the same thing?)

As far as I can tell, the pressure is pretty constant at between 12-15 psi. How would I raise the pressure to 25 psi?
 
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Old 12-22-17, 05:28 PM
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Without knowing what you have I cannot tell. Pics would be very helpful.

An auto vent looks like a can with a silver cap on top and is always open to bleed air by itself. The ones you have to open manually are manual air vents.

If you google these things you can see pictures of them s you can identify what you have or go to

http://www.supplyhouse.com/ and type in air vents or follow the headings and get all the info on what you have.

In the search bar type in 1/8" air vents to see what's available.

Hope this helps a little.
 
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Old 12-22-17, 06:38 PM
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This reminds me of why I joined this forum over 18,000 posts ago. A member had added to his system, on the second floor. He was having continual air problems along with the noise. He had tried many different "solutions" and none of hem worked. Finally, someone told him that his circulating pump needed to be on the outlet of the boiler and pumping into the loop. That would have entailed a huge amount of re-piping.

I looked at the situation and suggested instead that he re-locate the expansion tank point of connection to the suction side of the single pump, a much easier job than moving the pump itself. He DID have a diaphragm type tank so it wasn't that difficult. His next post was, "Wow, the damn thing works!"

Your system is not as conducive to such an easy fix, but to fix your problem you will need to move the "point of no pressure change" to the suction side of the circulators.

When was this system installed?
 
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Old 12-22-17, 07:37 PM
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Thanks. The Runtal radiator I installed has a manual vent. As far as I can tell, the baseboard doesn't have a vent, auto or manual. And I don't see any vents anywhere else for this zone (and no auto vents in any other zone, either).

I was thinking the spirovent could allow air in if it's not working right, but before testing that idea, it sounds like I should try properly bleeding the system at 25 psi. I'm not sure how to do this. I've read countless tutorials on how to purge air from hydronic systems, but don't recall instructions on how to increase the pressure (or maybe I just missed something fundamental). If you know of a good step-by-step guide, please point me to it!
 
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Old 12-22-17, 07:47 PM
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With a conventional, non-diaphragm expansion tank you should have NO automatic air vents and the manual air vent(s) should only be used with an initial filling IF there is air trapped in the heat emitter. The air in the water should be removed either with an air separator or inside the boiler proper by special piping and then the air piped to the expansion tank.

To raise the pressure in the system you need to find the make-up water Pressure Reducing Valve (PRV). Some models have a hand lever that overrides the internal spring-operated valve and allows more water to enter the system. A few do not have this lever and if that is the case then you will need to loosen the locknut on the threaded stem and turn the stem clockwise to raise the pressure. Count the number of turns as you will want to return it to the original point.

If you post several pictures of the boiler and nearby piping it will help us to help you. Pictures need to be well lit and in focus or they are useless. Pictures from far enough back or using a wide angle lens are best, if we need close-ups we will ask for them.
 
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Old 12-22-17, 07:51 PM
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Furd - Zones 2 and 3 were installed as add-ons to a single-zone system when the house was remodeled about 15 years ago (by the previous owner). The boiler is probably from the 1980s or 90s, but the house was built in 1927 (and I'm guessing the cast iron radiators and baseboards in the old part of the house are original).

I'm trying to understand why moving the "point of no pressure change" to the suction side of the pumps would make a difference. How does having the expansion tank on the output side facilitate air entry?

Because I have 3 pumps, I'm not sure how this could be done except by moving the pumps to the output side of the boiler, which indeed would be a big job.
 
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Old 12-22-17, 08:00 PM
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Furd - Yes, there is a lever on the pressure reducing valve next to the makeup water inlet. In fact I remember using that to fill the system quickly.

So, to pressurize zone 3 and purge, I think these would be the steps:
1. Cut off the other zones by using the ball valves for zones 1 and 2 (there is one next to each pump).
2. Use the lever on the PRV to step the pressure up to 25.
3. Turn the heat on to zone 3, which will turn the pump on. Run until hot.
4. Turn off the heat, then vent the radiator.
5. Repeat 3 and 4 until no air comes out.
6. Set the PRV back to 12 PSI.
7. Open all the ball valves and run the system in all zones.

Does this seem right?
 
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Old 12-22-17, 08:03 PM
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It is a complex subject and I cannot due it justice here. Plus, I can't type very well these days due to a progressive nerve damaging disease. However, if you do a Google search using the term pumping away you will find a huge amount of reading material.

Yes, unfortunately, moving your pumps is probably the necessary thing to do and this is definitely NOT the time of year to be doing major re-piping jobs on the heating system. There MAY be an easier way, at least to get you through this winter, but I would have to see several dozen pictures of the existing system before making any real suggestions.
 
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Old 12-22-17, 08:06 PM
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By the way, here is the pressure relief valve.
 
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Old 12-22-17, 08:15 PM
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Steps 1 & 2 are fine.

Isolate Z3 and pressurize to 25psi but DO NOT turn on the boiler and DO NOT turn on the pump.

Bleed your zone with the pump off while maintain that 25psi in the zone.

When all the air is bled and you get a smooth stream of running water shut off the drain valve and shut down the feed valve.

You should still have around 25psi in the system when done.

Drain off some water until you get down to about 18psi.

Open up all zones, and put all valves back to normal. Start up boiler and test.

If bleeding was your problem this should take care of it.

Hope this helps a little.
 
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Old 12-22-17, 08:16 PM
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Sorry to hear about progressive nerve disease. That sucks.

Thanks for the Google tip. You're right, there's an astonishing amount of information on this (such as https://heatinghelp.com/systems-help...g-away-piping/). I wish whoever installed the system had read it! I guess there was no Google back then, though.

I'll post more pictures later. Thanks Furd and spott for all your help!
 
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Old 12-22-17, 08:21 PM
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Is that 1/2 inch line the make-up water tees into continuing up to the expansion tank? If so it really should be a 3/4 inch pipe and it would be better if the make-up water did not connect there. Then again, if it has been working okay all these years it is probably okay.
 
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Old 12-22-17, 08:30 PM
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Yeah, the yellow handle ball valve is in the line to the expansion tank.

The system has been working for years, but that doesn't mean it's been working optimally - there has been occasional gurgling noise, especially in zone 3.

I'll try the 25 psi purge soon.

Thanks again!
 
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Old 12-22-17, 08:42 PM
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Was the Spirovent installed when you moved in? That would indicate that there has been air problems on zone 3 for some time. The way that boiler is piped with the main outlet coming out the side tells me the air is released in the boiler proper where it then travels to the outlet on top with the safety valve and the line going to the expansion tank. That Spirovent is not doing any good and may be causing the expansion (really a compression) tank to be losing its air cushion.
 
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Old 12-23-17, 11:24 AM
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The Spirovent was there when we moved in (2007), so it was either installed during the remodel (2002) or at some point afterwards.

I tried the 25 psi purge, but I'm not convinced it got all the air out. For one thing, even as the pressure dropped below 18 psi, there were still bubbles coming from my hose up through the water in the bucket. (I managed to blow the safety valve, so maybe air got in during that). And I'm worried that the compression tank is now completely full of water (I don't hear a slosh when I jiggle it). But the system gets hot and runs at 15 psi, so I guess it's more or less working - but that radiator is still noisy.
 
 

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