repeatedly getting air into baseboard hot water - need to find root cause

frumpf

Hello - I have 3 zone NG boiler hot water heating. 1 zone (first floor) keeps getting air and the pump stops working. Have had multiple HVAC services, pump replace 2x, and they all bleed the system and then it works for about 2 months and then quits again. None of them seem to know how to diagnose to find and fix the root cause. Other 2 zones work fine; have never failed. System also has a "4th zone" superstore hot water tank. Appreciate any advise on how what might be the root cause, how to diagnose, and resolve. Picture of system attached. Thank you!

DCContrarian

Water is leaking out somewhere in the system.

DCContrarian

Sometimes you can find a leak by pressurizing a system with air, not very much, maybe to 30 PSI or so. Air makes a hissing noise when it leaks unlike water.

hot_rod

it could be the fill valve is not maintaining pressure as air bleeds out. What pressure in on the boiler?

Or the Sprio is stuck or plugged and not finishing the microbubble removal

mattmia2

i was hoping someone would have better answers, but the first thing to do is to shut off the water feed and see if it maintains pressure. a leak and fresh water with dissolved air is one way it can get more air but issues with where the automatic vent(s) are installed is another.

do you bleed the air out to get it circulating again or are you purging with a large amount of fresh water?

if you bleed a couple times and it still keeps coming back after you burp just the air bubble out then it is getting air in somehow. it is possible as @hot_rod alluded o that the auto air vent isn't working and the air that is in the system instead of getting removed collects in one spot until it can't circulate and you aren't actually getting more air but are just not removing the air that cam with air from purging or filling the system.

it isn't a circulator, that isn't a way it can become air bound.

Jamie Hall

At the risk of adding an obvious comment — the air can't get in once it's out unless somewhere in the system the pressure is less than atmospheric… the only other possible source would be the expansion tank bladder leaking into the system…

mattmia2

https://forum.heatinghelp.com/discussion/comment/1893119#Comment_1893119

or makeup water.

DCContrarian

https://forum.heatinghelp.com/discussion/comment/1893121#Comment_1893121

A hydronic system should require zero makeup water once it has been filled and the air has been purged. If it requires makeup water, it is leaking, and the leak needs to be fixed.

I don't like automatic makeup water at all. If you have a leak, it is much better in the long run to know that you have a leak and be forced to fix it, than to have it be masked by makeup water. My advice is to turn off the valve on the makeup water, take the handle off, and hide it.

If there is a leak, and makeup water isn't masking it, the pressure at the point of the leak will drop to zero once enough water leaks out. Points higher than that will experience a partial vacuum. If you have a partial vacuum there are a couple of different devices that will let air in, in particular a lot of automatic vent type devices will leak air under vacuum.

My guess is that there is a leak somewhere low in the system, either in a crawl space or similar where you don't notice the water, or at the boiler itself where the leaked water just evaporates. Air is then getting in somewhere. Where the air is accumulating is not relevant to where the leak is, it just where the air happens to end up.

HomerJSmith

What do you mean that the pump stops and air gets in? I'm kinda dumb, so if you could provide more of your thoughts, it would help. Why would a pump fail 2x? The black pump or one of the greens. Pics of the offending zone (circuit) would help, too. Does the problem occur when all three pumps are running or only when the offending pump is running? Take some pics of the boiler piping from different angles. What are the model #s of the pumps?

leonz

Remove the cap on the Schrader valve under the expansion tank and press on the valve and if there is water coming out of it; Bobs your uncle and that's part of the problem.

Auto fill valves are more trouble than they are worth and can cause problems.

Once you have filled a system and flushed the air out of it you should only have to add water in the event of changing a circulator or if you have a leaking pipe joint.

I would want to turn the thermostat all the way up and let the system run for a few hours and if first zone is hot you have solved the simple problem; do the simple thing first and see if the bladder tank has ruptured before you turn the thermostat all the way up on all four zones.

hot_rod

it takes a lot to destroy a wet rotor circulator, constant running without fluid movement over heats them, and dry running ruins the bushings, then they may lock up

HVACNUT

We can't see the system piping too well, but that boiler has internal Bypass and System circulators. So WM wants P/S piping when using pumps.

There could be cavitation if not piped correctly.

Kaos

Most auto air vents will allow air in under vacuum conditions.

If your expansion tank is undercharged or has failed, when the boiler cycles off, the pressure can drop low enough to pull in air through an auto air vent.

You could set up an old cell phone to do a time lapse of the boiler pressure gauge. If the pressure is all over the place, the problem is with the tank or tank charge.

DCContrarian

https://forum.heatinghelp.com/discussion/comment/1893153#Comment_1893153

I like this scenario better than the one I proposed. System heats up, sheds water through the pressure valve, cools off and sucks air through the auto vent. Continues until enough air is in the system to act in place of an expansion tank.

frumpf

All thank you for taking time to consider and provide the advice. Much appreciated. I will think this through and while I will not tackle myself, gives me ideas to prompt HVAC service when they come.

HomerjSmith you asked some questions here are answers.

1. "pump fail" I was not so clear. Pump did not break, I mean the black pump has quit pumping 2x after being installed. I had 2 other pumps changed out - and they were probably working OK, but service tried to fix by replacing.
2. pump stops pumping and seems to be due to air since bleed fixes it for awhile, but then stops again after a couple months.
3. black pump is the one that has the problem. other two green ones have worked fine.
4. the problem occurs whether one or all circuits are being called.

frumpf

I appreciate the info and advice. a number of comments on likely water leak. A follow on question. If I do have a water leak and air is coming in with makeup water, then shouldn't the spirovent purge that air and I"d be OK? Would this suggest perhaps 2 issues - a leak and spirovent not working properly?

hot_rod

the flow needs to move through the Spiro 15- 20 times to do a complete job

If a big enough bubble rises up into the system it may not make it back to the Spiro

In that case you would need to purge from a purge valve to pull a big bubble back down

In some cases air purger vents get stuck, if you hear air in the piping, you should hear air hiss from the Spiro occasionally?

mattmia2

The spirovent could be stuck closed or clogged or have a plug/cap in the otulet, i can't tell if it is open to the atmosphere in your picture. Although unlikely, air could come around in a big enough slug that it fills the chamber in the spirovent and airlocks the pump all at once. since that is the first zone after the spirovent that is certainly a possibility. It looks like a bunch of air could hang out in the coil of the indirect unless you were carful about how you purged it.

hot_rod

I think that indirect has a 3/4 coil, so it takes a good flow to first purge them, being low go the boiler they can be tough to purge. Air, hot air, like to rise up to high points.

GGross

the pump on the left is a grundfos either upse or alpha? looks like it anyway. those have a dry run protection feature, not that they are perfect but it should just stop pumping when it detects no fluid to protect the motor. Is that what was happening?

mattmia2

I meant earlier that if you are purging (vs bleeding), flushing fresh water through to get most of the air out, there will still be small amounts of air trapped places and all that fresh water will contain dissolved air which will also come out of solution as the pressure is lowered and the temp is raised, that air should be removed by the spirovent but if the spirovent isn't working it may just collect and find its way to the circulator.

If the spirovent isn't working it will still collect the air but it will spill over in to the manifold once the chamber in the spirlovent is full so that may fill over time then when the circulator starts it moves that air bubble over to the veloute of the first circulator.(or possibly the combined flow of the other 2 zones can pull the air over where it rises up in the first zone which is off and gets stopped by a flow check in the circulator.)

Jamie Hall

I have to admit that I find it very hard to buy the idea that all the air problems are coming from the makeup water, unless there is just an awful lot of it. And I still wonder — and haven't had a reply — what the pressures are in the system at all possible leak points when the system is running.

The spirovent is one, true — but the pump seals are another, as are all the valves.

If possible, I would like to know the system pressures cold, and also system wide immediately on a cold start.

tcassano87

maybe a stupid question at this point in the thread lol but do you have bleeder tees on your baseboards? Have you taken the covers off and checked for any possible leaks in there

mattmia2

https://forum.heatinghelp.com/discussion/comment/1893289#Comment_1893289

think about what happens if the vent on the spirovent is closed or plugged. the air will collect in it then move along and airlock the first circulator. it wouldn't take a ton of air to airlock that pump if it has a flow check and the other zones pull a slug of air out of the spriovent while the black circulator zone is off

HVACNUT

@frumpf , can you post some pics little closer so we can see how the boiler and zones are piped? Is it piped Primary/Secondary?

mattmia2

https://forum.heatinghelp.com/discussion/comment/1893294#Comment_1893294

looks to me like it is just supply and return manifolds along the back but we need better pictures

hot_rod

it looks like a Webstone P/S tee valve left of the circulator?

But the black speedy headers don’t make sense?

Could be a mis piped P/S

pedmec

You need way more pics. I can't even see the boiler circulator.

Tom_133

https://forum.heatinghelp.com/discussion/comment/1893308#Comment_1893308

The boiler circ is in the boiler.

leonz

Do you mean the circulator is pumping into the boiler at one of the sump tapping's?

If so where is the suction line in relation to the rest of the plumbing?

HVACNUT

https://forum.heatinghelp.com/discussion/comment/1893354#Comment_1893354

There's two circulators in the boiler.

There's also external circulators. That's why we need to see the piping.

leonz

That mess makes me even more happy to have a single loop and one circulator.

hot_rod

that boiler has a thermostatically controlled bypass circ for return protection

In some instances it can be direct piped, the manual shows direct and P/S along with recommendations for the choices

It sort of looks like a P/S injection into parallel piped distribution?

DCContrarian

Two questions that would help us a lot figure out what's going on:

1. What is your system pressure when the system is hot?
2. What is your system pressure when the system is cold?

Bonus, extra credit: is the makeup water on?

frumpf

A few added info…

1. the make-up water was on. But I closed a couple of days ago and P has held steady over 2 days.
2. P when hot about 16.5 psi
3. P when cold about 15.5 psi

mattmia2

if it is holding pressure my bet is on air that never got out, the spirovent is broken or blocked off and it is collecting and directing that air in to the first circulator. you might have to burp it out by loosening the upper flange on the circulator a little but if there is a flow check it might not come out(and i would expect it to have a flow check because it is zoned by circulator)

the expansion tank appears to be good too because it is keeping the hot pressure down, unless there is just an air bubble somewhere serving the same function.

HVACNUT

https://forum.heatinghelp.com/discussion/comment/1893599#Comment_1893599

That's nice. Pics.

leonz

https://forum.heatinghelp.com/discussion/comment/1893599#Comment_1893599

Have you turned the thermostats all the way up to purge any air trapped in the system yet?

4Johnpipe

Check for a defect in the spiro vent. Check or replace the manifold union just passed the spiro vent. I have seen systems pull air in when the boiler / system water cools and exerts vacuum on the piping. A small defect in the union could permit air intrusion under this scenario.

jdirenzo

I wish I could see the the piping better. That is a terrible installation for servicing

CSACH

If your on a well you might have a bad check at the pump and when the system refills it gets a burst of air.

A failing circulatir can suck air through the shaft seal.

You have a leak somewhere possibly the boiler seals or a bad solder joint.