Air problems- how to diagnose

spudwrench2

I've got a hot water boiler and panel radiators. I can manually bleed the air out, but it reappears quickly- still heats OK, but gurgling noises, risk of corrosion, etc. I can't figure out where the air is coming from. 

I just installed a Laars JX-75 boiler. It's piped P/S. I piped it per the mfg's diagram for the JX-100, as they didn't have any examples of P/S piping for the smaller boiler.

There's a Spirovent Jr, a diaphragm type expansion tank and feed valve at the PONPC, the secondary circ is pumping away. The Spirovent, expansion tank and secondary circulator are all about 18 y/o. Primary circ is brand new.

There's a single zone for heating and no DHW. Near boiler piping is black pipe. It's piped 2 pipe direct return to 8 Myson panel radiators, the mains are 1" copper with the exception of the end-of-the-line rads which are piped in 3/4" copper. IIRC, there's about 100 equivalent feet of pipe including the fittings. There are no auto air vents, just manual key vents at the rads and the spirovent at the boiler.

Static pressure is about 15psi cold. All the piping is exposed in the unfinished basement, there are no leaks.  I do have one rad valve which is a bit crusty, but never wet. I convinced myself that air was getting sucked into the spirovent when the secondary circulator started up, so I threaded a valve on the air fitting on the spirovent and closed it.  Air issues continued.  I'm thinking that the air has to be getting in on the suction side of one of the circulators, but I don't understand how everything can be dry if there's some sort of poor seal somewhere. Any suggestions for figuring it out?

I attached the mfg's piping diagram I used...just mentally delete the second zone, the DHW section and the auto air vent.

hot_rod

Indirect tanks can sometimes harbor air bubbles that don’t get back to the spiro easily

Did you do a good high pressure power purge? 25 psi, plenty of flow? Panel rads need a good blast to move air from all those passages.

Do you hear air coming out of the Spiro? If not, maybe remove the top and make sure the float inside are not hung up. Whenever you hear air in the boiler room piping, you should hear the spiro hissing every 30 seconds or so as it collects those micro bubbles.

I prefer the air purger on the boiler piping, the hottest temperature, but it should eventually catch air in the loop also.

I’m not seeing any place where air could be sucked in, like sub atmospheric conditions with high point auto vents.
Depending on the pressure drop of the coils in the indirect, I suspect that is the lowest pressure point when everything is running, but not below 0 psi😚

A few other tricks, crank the boiler to 185 for a few hours to displace air. The higher the temperature the easier for air to come out of solution. Some installers add a few drops of dish detergent to collect air also, a famous Eatherton trick.

spudwrench2

Thanks for the response, Bob. I've seen a few of your "Coffee With Caleffi" videos. There isn't an indirect, just the one zone of heat, I did mention no DHW, but it's buried in my wall-o- text. So, that's one less place the air could be hiding!

It's sounds like you think that there's existing air trapped in the system, rather than any new air getting in.
I didn't do a power purge, just opened the bleeders until everything was filled up, treating them like cast iron rads. Hmm.
I am a little suspicious of the Spirovent... it hissed and spat a bit when I first fired up the system, but has been silent since. I'll check it and perhaps add some soap if I open up the system again. Thanks again. Will report back with results eventually.

STEVEusaPA

Let's see some picture of the entire near boiler piping.

spudwrench2

Here you go, please go easy on me. The return is on the far left of the first picture. The Taco 007 is the primary loop circulator (probably WAAY too much pump, but it came bundled with the boiler.)

The closely spaced Tees are about 7" on center. I used 1" pipe as that should be enough for the 63K output of the boiler, if I understand correctly.

The third shot is the most embarrassing- the totally out of plumb supply to the feed valve.
The Grundfos circulator for the secondary loop is also mounted upside down (they want the terminals facing down for some reason.) It operated fine upside down for many years with the old boiler. I'll fix that when it comes time to replace it, but was trying to not disturb the old flange seals as I didn't have replacements on hand.

Finally, the reason I used Tees with plugs rather than 90s is to allow adding an additional zone and circulator down the road.

hot_rod

Why the valve on the spiro discharge, is it leaking? If so, another good reason to pull the top and look inside.

Pumping away from the tank? looks fine. A pressure gauge on the system pump discharge would assure you are adding head. It would be interesting to watch that gauge with just the boiler pump running, just the system pump running, and both running.
I might have put the expansion tank before the boiler pump, but it should not be a issue for your air problem

Is that a Watts fill valve? it should have a fast fill lever or screw to increase pressure. I'd set it to 25 psi and do a purge at that higher pressure.

spudwrench2

The valve on the spiro discharge was for an experiment. I was thinking that maybe air was being sucked in through the discharge, so I closed it off. I'm going to order a replacement top for it, with the age of it I'm not confident that if I take it apart I will be able to get it to seal properly and I don't think I have an O-ring of the proper size. Might wait for the end of the heating season to do this.

I think I see what you're doing with relocating the expansion tank. That's so both the boiler pump and system pump are pumping away from the tank, yes? I thought I was safe following the boiler mfg's piping diagram. Are you suggesting that because you think the boiler pump is oversized?

I'm pretty confident the boiler pump isn't inducing much if any flow in the system/secondary circuit. I have temp monitoring probes on the main supply and return lines. When the boiler first fires, only the boiler pump turns on. I can see the boiler temp increasing (but the system temp doesn't change much if at all.) After the boiler heats up above 140 (?) and the system pump turns on, I can then see a rapid increase in system temp. The system pump runs for a bit, then the boiler temp gets pulled down from the cold return water, the boiler shuts the system pump off to prevent condensation, the boiler temp goes up again, etc. Don't really see much steady-state operation this early in the heating season.

hot_rod

I think your p/s is working okay, no induced flow 4D, 4 pipe diameters between the tees is max. Which boiler do you have, I suspect 8- 10 gpm is what you are flowing?

I'm leaning more towards the Spiro not working, or working well. They do get sludged also, preventing the mesh from working adequately.

I don't think the tank location is a deal breaker, the manual shows it like you have it.

In a perfect hydronic world I would have both the air purger and exp in the boiler line not the distribution for best air removal, hottest point in the system. I see a lot of vertical air purgers used in piping like yours.

spudwrench2

I've got the JX-75, that's 63K BTU output, so if your estimate of about 8-10 gpm in the primary loop is right, that will line up with a 15 deg or less delta T on the chart.

I'd consider trying one of those vertical Caleffi air purgers in the primary loop- it would just go on the hot output of the boiler, right?

Thanks again for your time on this! I'll check back in when I've done something or have a result.

spudwrench2

An update! The first thing I did was to disconnect a radiator valve (there's one rad that's able to be isolated from the rest of the system via ball valves- long story) and add a drop or two of Dawn. That, plus repeated manual bleeding greatly improved things. Made it through the -9 weather OK in the luxury of hydronic comfort...
Based on Hot Rod's suggestion that the Spirovent jr. wasn't working effectively, I bought a new one. I considered his suggestion to install a vertical air sep in the boiler output, but that seemed like too big a project to tackle mid-heating season. Decided to just swap the top and the element/core. The new element had a green plastic plug in one end, the old element didn't. Unfortunately, I didn't notice the orientation of the plug when I was pulling the new Spirovent apart, so I had to guess which way was up.
Does anyone know what the plug is for and which way it goes?
While the system was open, I checked the expansion tank... it read 7psi and a small amount of water came out of the valve. It's definitely not filled with water which I understand is the usual failure mode. ANYWAY, I swapped it out for a new tank. After refilling the system things seem to be working well. I still have some panel rads which are pitched the wrong way and trapping air I need to correct, but that will be a project for the spring.

mattmia2

If the air separator is working right the pockets of air should eventually find their way to it and out, no need to have everything pitched perfectly as long as you can get enough air out to get flow started.

EdTheHeaterMan

The Expansion tank with 7 PSI and a small amount of water on the Air Valve side is a big clue. You were probably loosing small amounts of air from the tank into the system over the last few weeks. I believe the new tank will solve your problem. You just need to allow the Spiro-vent to do its job for a few days/week.
I think the green cap is the bottom.

hot_rod

What could and did happen in Spirovents is a fast fill flow would push the float inside up, and off, and they did not vent air well during the initial filling.

The green plug eliminates the straight up flow potential. The explanation from a rep, and it certainly makes sense when you ponder it.

Seems it should be on the bottom so pressure from the fill keeps it in place.

spudwrench2

Dagnabbit, I had a 50/50 chance of getting the orientation of the plug right and I lost! I think I'm going to let it ride...

hot_rod

I think to top of that mesh goes up against that perforated stainless disc inside, so it is probably safe.