Constantly purging air in hydronic system

T. J.

Grundfos UP 15-42F

BTW, I have the system drained now until a plumper can come. Since I'd like to be home, the only time our schedules mutually meet is in a couple of weeks. Is there any harm in leaving the system for that time or am I risking corrosion in the boiler? Should I partially fill the system? Just a thought I had.

icesailor

Water Deposits:

Steam Irons for ironing clothes require that you use distilled water so as not to get deposits inside and ruin them. Even so, they still gat deposits from the boiling water converting to steam vapor. Distillation doesn't get all the potential deposits out.



That apparent leak is so slow that when new, if you pumped the system to 100# air pressure, it probably wouldn't show a leak because the solder paste would hold the air back. Once hot water hit it, the solvent action would clean out the flux. The leak is so small that it wouldn't be noticed because being at the top of the system, there is the minimum amount of pressure. The amount of water that might leak out of that fitting is probably negligible. Now that you know it is there, put a container under it and watch it until you get around to fix it. Don't worry unless it leaks badly. Pump the system up to 15 to 18# and let her rip.

If you drop the system to zero, and tale about a gallon of water out of the system, and the leak is on the top floor, you don't need to drain the whole system. Just change the ell. Make sure that you don't try to patch it. It won't patch. Replace the fitting and well clean the pipe. You will notice that there is a large spot on the fitting and/or pipe where the solderer started at the top and soldered the top of the fitting, then switched to the bottom. Leaving the middle of the ell not hot enough for the solder to flow. Heat rises. Always start at the bottom and solder UP. Wipe the goobers off with a rag. If the goobers don't wipe off immediately after you take the flame away, the fitting wasn't hot enough.

T. J.

Slow leak

Do you think the leak is so slow, that it couldn't be the root cause of a reduction in pressure of 5 - 6psi pressure in the course of a few weeks?

T. J.

Update one year later....

I just wanted to update on all the changes I had made to repair the air entrapment/air introduction issues I had been experiencing in the past couple of seasons. As a quick re-cap, the first thing I did after posting was read Dan's book, Classic Hydronics. Then, with the advice in that book, plus all the good advice on this thread, I made the following changes (with most of the work performed myself):

* Removed automatic vent on a baseboard unit at top of the system.
* Repaired leak in an elbow of the same unit.
* Installed Taco Hy-Vent with an anti-vacuum air vent cap on the air scoop.
* Relocated expansion tank piping from the supply side to a tee on the return side and turned the tank right-side-up.
* Moved the city water make-up from the supply side to the expansion tank's tee on the return side.
* Installed a back-flow preventer.
* Replaced the malfunctioning tridicator.
* Repacked all leaking valves.
* Set the expansion tank and the pressure reducing valve to 18 psi.

The results? Well, all last winter I only had to purge the system once and that was right after the initial purge (I must've not purged all the air, initially). All summer the system sat idle. Then last night I fired it up and there are no issues and no air entrapment.

Thanks all.

T. J.

Mandinka

Not sure if I should start a new thread or not since I also have to constantly purge air, maybe every few days. Reading through these posts I learned that fresh city water will cause air to become trapped in the system once heated and if the pressure in the system is too low the air circulates causing gurgling and air locks.
My system is three zones.
Basement, first and second floors.
The furnace, honeywell zone valves, bleeder valves are all in the basement. My radiators are all in series, (not parallel) so I can not isolate individual radiators within a zone. None of my radiators have bleed valves so when the posts say "bleed the highest point" or check the pressure at the highest point, the highest point I can do that is in my basement which in my opinion probably defeats the object of the exercise.
The basement zone doesn't appear to suffer from the air, just the first and second floors which are both above all of the "workings".
Curious (to me) that the basement doesn't have a bleeder and although it is the lowest point in the system it also doesn't have air.
So....I purge the other two zones every few days and the air comes back. Why ? When running my pressure is around 18psi.
Should I replace the bleeder valves ? They look similar to honeywell FV180....I say look similar because that is the best picture for reference that I found. They are screwed into elbows in my system just above the zone valves before the radiator runs start.
Something like this : Boiler - expansion tank off to side - zone valves - bleeders - radiators - circulator - boiler.

The system is currently on, pipes are gurgling, pressure guage on the furnace reads about 18psi.

If I purge then shut the bleeder valves will that allow me to eliminate them as a problem or is that a no-no ?

Any help would be appreciated, I've been dealing with this for two winters now, coming up on three.

One last thing, maybe irrelevant. I put the heat on for the first time this year and there was hardly any gurgling, it seems to have got a lot louder in a few days.

Thanks.

Ironman

Can you post some pics of the boiler, it's near piping,mans the zone and purge valves?

You should start a new thread.

Mandinka

Ironman said:

Can you post some pics of the boiler, it's near piping,mans the zone and purge valves?

You should start a new thread.

Is it possible to post video ? It would be easier to describe the set up with a video than with pics.

davidnotaplumber

I realize the last post was now years ago, but wanted to add since I have a similar situation.
1. Have 2 loop hydronic baseboard heating system. About 40 years old. Lived here for 10 years. Also have another furnace with same type of system, bit bigger. It works fine.
2. In one system I have tried to purge the air many times, I am doing it correctly and have had 2 plumbers in to try an purge, last one who knew his stuff but 3 days later some of the air is back, it appears more in one loop than the other (?) not 100% sure this is true since the water does commingle in the boiler when both fire off at same time.
3. Last plumber replaced the feed, 14 psi feed valve. There were 2, one was old and I suspect did not work well and and other was just added next to it. I suspect 2nd loop has not been working well for 2 winters, just goes to a bathroom and seemed like it did not heat up as well as it should. Water does circulate well now and since first bleeding I did some time ago seems better. Also overall seems like less air in entire system since plumber bleed 3 days ago. Also I replaced the automatic air release velve on top of the air scoop, and new pressure relief valve on the top of the boiler was replaced by plumber.
4. Maybe the new water since last purge accounts for air working it's way out, but I sort of doubt it.
5. I wonder if there is a problem in the loop to the bathroom that seems to get the air and if there is how do I figure it out. the pressure in the system is good and no obvious leaks. Is it possible to have a tiny pin hole air leak with little water that lets air in the system? thanks for any help.

T. J.

I know my original thread is a few years old now, but I decided to post a follow-up question here since it does relate to the original problem....

This past spring, after reading Dan's hydronic book yet again and after reading some posts here on the subject, I decided to investigate the possibility of keeping the city water make-up shut off during the heating season out of boiler safety concerns (I do not have a low water cut-off). I thought that since I put so much effort into fixing air entrapment issues, I might have a sealed-enough system to safely make this change. However, first I thought I'd perform a leak test over the summer. After shutting down the boiler for the season, I shut off the valves to both the city water feed and the expansion tank circuit, but not before pressurizing the system to 20 psi and leaving it.

Well last week, four months later, I went downstairs to get the the system up and running and the pressure on the boiler's tridicator indicated only 10 psi. Not totally depressurized, but enough that I believe parts of the circuit on the second floor went into vacuum as there was audible air bubbles after the system first cycled.

My long-winded question is what is the consensus on the size of this leak? I can't seem to find it after all this time. I guess it could be in the walls or between floors, but that has me worried that it's rotting my house from the inside.

nicholas bonham-carter

I don’t see how there could have been a water leak, if there was positive pressure, and air in the system, which must have been there when you shut down the system, and shut off the inlet valve.
It may be a leak in the expansion tank of air through the diaphragm.
Can you trust your tridicator gauge?-NBC

clammy

Do have any piping that is ran underground it was quite common years ago to run the basement loops in concrete ( cheaper and quicker) when you re bleed the 2 Nd floor are you doing into a bucket and what s the water look like if it’s orange it rust and you defiantly are taking on water and have a leak . Peace and good luck clammy

Jamie Hall

The expansion tank was definitely valved off? If so, you're asking an awful lot of a system full of joints and seals to hold pressure over a summer. A loss of only 10 pounds over that period of time, in an otherwise sealed system, is minor. That said, it probably did put the highest points in your system into a slight vacuum, which probably did pull in some air (water would have been standing some 22 feet above the gauge to give that pressure -- if the gauge is accurate).

I'd have left the expansion tank open to the system, to avoid just that sort of problem.

T. J.

Thanks for the comments.

I didn't think about potential diaphragm leaks in the expansion tank.

I intentionally shut the expansion tank line because I thought it would more immediately show leaks, if present.

As far as tridicator accuracy is concerned, I know they're never that accurate, but I installed a new one a couple of years ago when I re-piped the feed water and expansion tank lines to the boiler.

There are no pipes in concrete. Boiler is in the basement and water is piped up to baseboards and fan-convectors on the first and second floors.

When purging, water that had emptied from the boiler was quite clear.

Jamie Hall

Well, shutting off the expansion tank will indeed show leaks faster... and magnify, many many times the effect of even trivial leaks. Water is essentially incompressible, as are the pipes -- but not quite, so even the loss of a milliliter or so of water will show up as a large pressure change...

In this case, though, the test is really inconclusive, as the pressure dropped low enough so that you may have had a vacuum in the highest radiators -- and their valves. If there was a vacuum leak in that area -- quite possible -- and any leakage was low in the system, instead of dealing with the large pressure change with small volume change of the virtually incompressible water and pipes, now you are dealing with the pressure change from the dropping water level in the pipes. A very different rate of change with volume.

If you really want to test for a very small leak, you need to bring the system up to pressure and purge thoroughly -- no air left at all -- and then close off the expansion tank and watch the pressure change over a short period of time -- an hour or two will be ample (longer is problematic, because the pressure will also change with temperature). If everything is holding, the pressure shouldn't change much -- a pound or two, perhaps.

T. J.

Okay, thanks for all the advice.

I thought I was being smart and it was going to be a robust leak test with the expansion tank isolated, but I guess I need to redo and maybe invest in a good gauge while I'm at it and not rely on the tridicator.

bls

A chemist in my church suggested a possible solution to a similar problem that I’m having. He said that it’s possible that my system- maybe yours as well- has in effect created an electrolytic cell, like a chemical battery- within your pipes. He said (I’m not a chemist, so bear with me) that either dissimilar metal corrosion or this cell, could create a small amount of voltage and the bi-product of that reaction is a small amount hydrogen gas. As such, my system is only two years old and last year sprung a bunch of aggressive, corrosive-looking leaks and whenever my circulator fires up, the air scoop removes some bubbles that had been growing in my boiler. Maybe that would explain why you have a leak and why you’re getting air at the same time. I don’t know how to fix it yet, but thought I’d throw that out as an option. I grounded my boiler with a separate pipe clamp to the EGC of my pump, hoping to ground out the reaction, to no avail. Good Luck!