Can't purge the air out of the boiler!

junta

I had a boiler tech out to clean and maintain our boiler. He purged the system, which ultimately made our highest zone extremely loud to the point it wakes up at night. Another guy came out and purged the system from a different drain valve and different method, which didn't help. He mentioned that the drain valves were not in the correct spot so, "This is as good as it is going to get." The system was installed about 25yrs ago and there hasn't been problems in the past with purging, so I am not sure if that is the case.

I have tried to purge several times and it seemed to be successful. No more bubbles were leaving the hose and the zones were quiet, until the problem zone would kick off at night. When it would come back on early in the morning, a super loud rushing water noise would come followed by pretty constant air bubbles. I am trying to figure what could be going wrong.

Where should the system be getting purged from and what should the process be since I have seen several methods now? What could cause the bubbles to be returning after the purging seems to have worked? I don't see any physical leaks and when I shut down the boiler to cool so I could purge, the pressure maintained, which seems like a leak isn't present.

Any help would be great so we could get a good nights rest. Thanks!

STEVEusaPA

You have more than all the shutoffs and drains you need to easily purge the system.
I don’t like the circ on the return or the air scoop, but it worked well all these years.
Purging is the first part, air elimination is the second part, and it appears you don’t have proper air elimination.
Do you have any air vents any where else in the system?

HVACNUT

I originally thought no problem. Then realizing the returns come up from the floor, it's not piped correctly.
There needs to be a purge station installed on the return, just above the PRV.

STEVEusaPA

@HVACNUT Take a look at the pic. Doesn't this purge a zone?
Red lines are closed valves, blue is flow of water. Of course the zone valves need to be manually opened.

junta

There is a hy-vent on the top of the air scoop is the only air vent, which I don't hear much hissing coming from the vent as the purge happens. It is brand new because the last Taco was leaking. Being a hydronic system, should there be vents located elsewhere?

HVACNUT - I once had a boiler guy tell me that the system was backwards when he was out at the house, but he didn't say anything more. To understand you, the side the expansion tank is on should be the return, but it isn't? So your suggestion would be to put in proper drain valves just above each of the zone's yellow ball valves on the right side, which is where I should hook my hose up at? I was purging from the red drain valve below that, the last boiler guy told me to purge from the blue valve right above the 3 electric zone valves.

SuperTech

The expansion tank should ideally be on the supply, with the circulator after it. For best possible air elimination the circulator should be "pumping away" from the expansion tank. Your tank and air scoop being on the return is kinda backwards.

HVACNUT

> @STEVEusaPA said:
> @HVACNUT Take a look at the pic. Doesn't this purge a zone?
> Red lines are closed valves, blue is flow of water. Of course the zone valves need to be manually opened.
> (Image)

Yes, of course you are correct. The old backwards purge ploy. I didn't notice the ball valves on the supply.

Jamie Hall

Just for the sake of laughs -- check your system pressure. Air can't get in to a system unless -- somewhere -- the pressure is less than the atmosphere outside (although a small amount of air will appear in a properly purged system from the water itself -- hence the air eliminator). If you system pressure is too low, particularly if you are pumping towards the expansion tank, that can cause recurring air problems.

HomerJSmith

You need to add one more valve to effectively purge the boiler.

A ball valve can be added on the supply out of the boiler before the zone takeoffs or a Webstone valve can be added on the return before the supply water pressure regulating valve. I assume the return pipe is 1 1/4".

https://www.supplyhouse.com/Webstone-50615-1-1-4-SWT-Webstone-PRO-PAL-Ball-Valve-w-Drain

Purge one zone at a time. Either use a purge pump or street water pressure. Either of these may open the boiler pressure relief valve if the supply isn't shut off before the drain is shut off.

junta

@HVACNUT In your photo you have the ball valve closed below the auto fill. Should the ball valve on the return (behind the flue and before the water temp gauge) be shut as well? So no water is leaving or entering the boiler? With my setup being backward, is there any harm to it or just not the most efficient setup?

When I let the boiler sit off the other day and started to purge, the pressure was sitting at about 20.

STEVEusaPA

The boiler system can be purged basically as shown in my marked up picture, one zone at a time. When your done the zones, you can open that valve by the fill, close all the other valves, and purge the boiler.
Then it will work fine.
It is pumping away from the expansion tank, but air elimination should be a modern micro bubble resorber, installed where water is the hottest.

mattmia2

Is the cap open on the automatic vent so it will actually allow air to escape?

junta

When you say purge the boiler, do you mean moving the hose to the drain valve under the pump and then purging from there while the auto fill refills the boiler? Yes, the vent is open.

SuperTech

> @junta said:
> When you say purge the boiler, do you mean moving the hose to the drain valve under the pump and then purging from there while the auto fill refills the boiler? Yes, the vent is open.

> @junta said:
> When you say purge the boiler, do you mean moving the hose to the drain valve under the pump and then purging from there while the auto fill refills the boiler? Yes, the vent is open.

You have to use the fast fill handle and manually raise the pressure to properly purge each zone, the 12-15 PSI pressure the auto fill reduces the pressure isn't always enough to force the air out.

STEVEusaPA

Close all the shut offs in red to the zones, purge the boiler via the blue.
Then I'd run the circ a little bit thru all the zones, and purge it again.
You may want to purge the boiler first.

STEVEusaPA

Now that I take a look at the other photo, purge the boiler first as mentioned, then purge each zone like this, remember to manual open the zone valves.
Also, the circulator is off when you purge.

junta

Ok, thanks everyone for giving me some feedback. I will let the boiler cool tomorrow during the day and then purge after work using the method above. That is not a method that I have seen used on the boiler yet, so maybe it will be the miracle shot. I attached one last shot from a different angle incase this helps provide any more info.

junta

I purged the boiler and then the zones from the recommended drain valves. Got a lot of air out during the boiler process and not too much out from the zones, maybe because I had just purged the zones. There is no more gurgling noise in that problem top zone, but there is the sound of flowing water now. Whenever that thermostat kicks on for that zone, water sounds like it is filling the pipes again, pretty loud at first and then slows to a trickle. The trickle is loud enough to keep us up at night, to the point we just shut that zone down. Is there still air in the system or is something else going on?

hot_rod

What is your final fill pressure, co
Be sure you have an accurate gauge to read it, you can screw one onto a purge valve to confirm the boiler gauge is accurate.
Two story home you want 12 psi minimum, sometimes adding a few psi will help eliminate that final air.

Is the brass air vent on top of the purger functioning? Sometimes you can loosen, not remove!, it and see if air comes out around the threads. Could be the brass auto air vent in not working properly.

Hot water gives up air better, sometimes it takes a days worth of circulation, especially with a simple air scoop device.

With the expansion tank on the return, air elimination becomes more of a challenge.

mattmia2

A little more pressure would ensure it doesn't go in to vacuum anywhere as well. If you hear water flowing and there is not any air in the zone you probably have an oversized pump which will be more likely to pull some of the system in to vacuum, especially if the pump is not pumping out of the expansion tank.

Solid_Fuel_Man

Have you tried bleeding any radiators since this last purge?

Edit: not sure if you have radiators as I reread this post. I may be confused with another thread.

EdTheHeaterMan

Ok so everyone is clear From what I see the circulator IS pumping away from the expansion tank. the Taco 007 circulator is not going to be too big to create a vacuum or lower pressure in the system below atmospheric pressure, because the point of no pressure change is on the inlet side of the pump. The water feed is in the same pressure zone as the expansion tank (point of no pressure change). since the expansion tank is fairly new the assumption is that the tank is properly pressured at somewhere near 12 psi. (But that should be checked). The only small problem with best practice install is the location on the return, but that has not been an issue for years. So what has changed?

Has any other repair been made since the expansion tank replacement?

I'm with all the members that indicate the pressure may be low!

Double-check the Air pressure in the bladder tank and the pressure setting of the Watts 1156 feed valve and verify the boiler gauge with an independent gauge.

Since the air scoop does not have at least 18" of approach piping as indicated in the installation instructions, it will function very slowly to purge air from the system. Also, you won't get the help of Henry's law and Boyles'law's of the physics of water to help eliminate the air. You need to get it done by pressure purging through the highest loop with the highest pressure you can get to entrain the air in the upper zones and force it down the pipe from the higher floors. This may only be 26 to 28 PSI because the pressure relief valve will release at 30 PSI with the current piping.

the air is not going to MOSSY ON DOWN the pipe. You need to push it with speed and volume.

Solid_Fuel_Man

On pesky systems, you can turn the boiler off and run one zone at a time for several hours. Then turn that thermostat down and move on to the next zone for several hours. This is all after you have confirmed good system pressure and proper air charge on the expansion tank. If the boiler is off (turn off the gas) then you dont need to worry about overheating the house one zone at a time.

STEVEusaPA

Keep in mind you're probably overpumped for just one zone calling, could be the reason for the noise, but if properly purged, you'll hear very little water moving.
If you kept the pressure up in the 20 psi range while purging, and do it like shown in my marked up picture, all your noise should go away, as well as initial air as you have no real air elimination.

hot_rod

If the circulator is pumping into the boiler away from the expansion tank then the air purger is in a bad spot. Best air elimination is at the hottest point in the system, close to the boiler outlet or supply as possible.

Even in the proper location, with proper piping those "camel hump" struggle to catch and eliminate the micro bubbles.

So every time the boiler warms air is driven out of solution, when it cools that air goes back into solution if not eliminated.

ch4man

I have a hard time with that picture Hotrod, I have been inside of a working boiler before.
ok, thats a stretch.
my ex-no brother good-in-law used to have a wood burning hot tub. aluminum fire box that sat right inside the hot tub next to ya. even with a rip roaring fire of a wheelbarrow of oak wood you could still place your hand on the firebox under water.
so that micro layer of water thats hot enough to cause microbubbles must be really, really thin.
not saying the micro bubble dont form there, but its odd its "steaming"

hot_rod

ch4man said:

I have a hard time with that picture Hotrod, I have been inside of a working boiler before.
ok, thats a stretch.
my ex-no brother good-in-law used to have a wood burning hot tub. aluminum fire box that sat right inside the hot tub next to ya. even with a rip roaring fire of a wheelbarrow of oak wood you could still place your hand on the firebox under water.
so that micro layer of water thats hot enough to cause microbubbles must be really, really thin.
not saying the micro bubble dont form there, but its odd its "steaming"

I suspect it is the relationship between the water around it and the size of the heat exchanger surface area. Any creosote issues? Dropping below 250F creosote will condense on the surfaces. Between 150 and 250 it will be a liquid.

Common gas fired hot water tanks are built with"sloppy" or inefficient heat exchangers so a plain steel tank and flue passage can work for many years at condensing temperatures. Consider 55F or colder water entering the tank, and some tanks operating at only 120, well below the fuels dew point. You'd think they would sweat gallons of water. The high flue temperature with the inefficient HX is the key. Also why they run mid 70% efficiencies, on a good day

If that wood fire box was surrounded by 20 gallons instead of 500 gallons of water you would probable see hotter wall temperatures.

In a boiler the cooler that metal exchange surface the less minerals precipitate from the water, so with a mod con designed to run low temperatures the lower temperature not only increases efficiency, but also lessens scaling potential, a double win.

The pic is just an example of the thermodynamics taking place, your numbers may vary.

A simple pot of water on the stove is another visual example of how those micro bubbles appear on the bottom almost instantly when the burner is fired.

mattmia2

Ideally you would remove those bubbles as the heat from the boiler and lower pressure from the pump both work to make them form then the deareated water cools in the heat emitter and picks up the last of the air in the emitter then it gets squeezed out at the boiler. when the air eliminator and pump are before the boiler and when it is a less effective air eliminator that doesn't happen as effectively.

junta

Ok, so from the feedback it seems like my next step should be checking pressures. I was told my gauge needs to be replaced because it was showing pressures over 30 and my pressure relief valve wasn’t opening, although the valve was working fine manually triggered. I was going to save that for a future post question.

Some other notes:
- my vent caps is open and I do hear some hissing of air. It was replaced a few weeks ago due to the old one spewing water.
- the boiler guy was out about 2 months ago to do routine maintenance/cleaning and since then we have had these issues. The system never had this much air in it or the 10mins of rushing water in that top zone in the past 5 years we lived here.
- Even with manually opening the auto feed while purging, the psi stays around 20.
- I have baseboard heaters.

So my steps need to be:
1. Check boiler pressure by attaching gauge to one of the drain valves on the boiler.
2. Check pressure of expansion tank. Does it need to be removed in order to get accurate pressure?

Questions:
1. How do I check the pressure of the watts auto fill?
2. Should I be purging when the system is cooled to reduce possible damage or does that creat additional issues since bubbles are going to be more present when the water is heated back up.

hot_rod

You can buy or build a test gauge to go onto a hose connection, like this. All these parts are at a wholesaler, ACE, or box store.

I like a large face 30 psi gauge to detect small pressure movements. Switch the hose adapter to a 1/2 fip and use it check and confirm the expansion tank pre-charge pressure. Using one gauge for all measurements eliminates that error. This one has an air stem for pressurizing and air testing systems also.

Check the boiler fill pressure with nothing running, that is the static fill pressure.

yes the tank needs to be removed to test the pre-charge, add an isolation valve when you reinstall. Webstone makes a nice one with a drain cock and and iso valve all in one.

STEVEusaPA

For system pressure Watts sells a hose bib connection on a pressure gauge, or you can just get this 'Add-a-Gauge' from Webstone.

And while you're at it, get one of these for the expansion tank, then you'll never have to drain the system again to check the tank:



And while the system is drained, replace the relief valve.

junta

Thanks for all the advice to update my system. I will definitely get those valves installed and replace the pressure relief valve. I do have a Rainbird pressure gauge that I attached with the boiler not running and nothing was registered. Thinking it was broken, I attached it to my hose bib and got my normal city water pressure reading. The gauge starts at 20, so I wonder if the static boiler pressure is below that? I bought a new gauge and am waiting for it to arrive to compare pressure and then test the pressure of the expansion tank.

junta

So, with a new gauge that starts a 0, my static pressure remains too low to register and the needle stays on 0. The expansion tank registers at 9. I assume I need to pump the pressure up?

Do I need to adjust the Watts auto feed? If so, I am unsure how to do that because it doesn't have a screw as other models show online.

SuperTech

Expansion tank should be 12-15 PSI when there's no pressure on the boiler. I would add pressure to it, or replace it. You can adjust the Watts pressure reducing fill valve, but those don't last forever either. I'd replace the tank, fill valve, pressure relief valve and all of the air vents. It's best to re-trim the boiler while you have it drained. If you have a pressure problem it's best practice to replace the pressure controling devices. That way you can limit the amount of times you have to drain the boiler and add fresh water and air into the system.

hot_rod

looks like the lever is missing from that Watts fill valve? The lever lifts up, depress that stem you see for fast fill. Also for adjusting fill pressure.

Solid_Fuel_Man

There is your problem! Your auto feeder may be clogged. Are you sure the valve is open to it allowing water to the auto feeder? There used to be a lever which pushed down on that brass rod sticking out. If you push on the rod you should hear water moving through the valve.

junta

Solid_Fuel_Man said:

There is your problem! Your auto feeder may be clogged. Are you sure the valve is open to it allowing water to the auto feeder? There used to be a lever which pushed down on that brass rod sticking out. If you push on the rod you should hear water moving through the valve.

The lever isn't missing. Being curious, I just took it off to see if it had a screw adjustment or not and it is now back on. When that zone was turned on this morning and I was hearing the rush of water for 5 mins, I was thinking that it seems like the water level is low which is why there is such a big movement of water. So maybe the auto fill isn't putting water back in correctly after the purge? Would this even make sense?

SuperTech said:

Expansion tank should be 12-15 PSI when there's no pressure on the boiler. I would add pressure to it, or replace it. You can adjust the Watts pressure reducing fill valve, but those don't last forever either. I'd replace the tank, fill valve, pressure relief valve and all of the air vents. It's best to re-trim the boiler while you have it drained. If you have a pressure problem it's best practice to replace the pressure controling devices. That way you can limit the amount of times you have to drain the boiler and add fresh water and air into the system.

I will replace the auto fill and other components and see what happens from there.

Even though I had a tech (who originally started all of these problems for me) tell me that my pressure gauge was not operating correctly, would it be safe to assume that my gauge may be operating correctly and my relief valve has been opening when the gauge has been spiking over 30 when first heating up? The pipe from the relief valve doesn't have an air gap and enters into a larger pipe to drain across the room to a floor drain. So I can't visually see if it has been dripping or not.

HomerJSmith

If you are trying to fast fill your sys with that lever on the Pressure Regulating Valve, it probably ain't gonna happen. You need water flowing at least 2' per sec to move air down a vertical pipe. That means a high flow rate.

If you are using street water, connecting a garden hose to your sys from a hose bibb would be a better choice. But, you need to shut off the hose bibb before shutting off the boiler drain or you will force water out of the Pressure Relief Valve on the boiler.

Since, you have ball valves on each zone, you could close all the zones except the one you are charging and do each zone one at a time. It would be easier by adding a valve like I said in my earlier post.

SuperTech

I believe that once you replace the expansion tank, fill valve and air vents and give the zones a good purge you will be good to go. Definitely replace the relief valve while you have the boiler drained. They are inexpensive and a very important safety device. You can add a few drops of Dawn dishwashing soap to the boiler as well. This will help the air vents to do their job.

junta

Well I bought the wrong relief valve because I needed a female valve for my setup. I really don’t want to wait to have a new one delivered. Is it acceptable to use 3/4 female connector and is that something a box store would carry? No plumbing stores are open on the weekends around here and I want to replace the valve ASAP.

mattmia2

yes.