Home hydronic heat help, purging air

[spaceman]

My weekend mountain place has a hydronic heating system - 'between the joists' pex tubing with a small boiler and 5 separate zones (1500 sf 1 1/2 story house with crawl space). It's 17 years old, but pumps, zone valves, mixing valve have all been replaced within the last few years by a local plumber. The glycol is also only a couple years old. The only 'old' part is the caleffi air vent on the top of the air scoop, so I will get a replacement for that since it is a $9 part and it seems like cheap insurance in case that is part of the problem.

The plumber has retired and moved to Creede, CO. I'm having trouble getting phone calls returned from other local plumbers.

Here is my current problem: system starts up, runs, and I have verified that fluid moves through the pex when a call for heat is made. However, it struggles to warm the place much over 63 or so degrees, with outside temps dropping to single digits at night. When is working right, it has no trouble cranking out the heat.

The main pump seems to be cavatating a bit, definitely not the normal quiet 'hum'. so I'm thinking there's air in the system. (I've had this condition in the past due to air in the system).

I've read up on how to purge air out of closed loop hydronics, and I'm pretty sure I can tackle that. I'm just wondering if there's anything critical that I need to watch out for when I'm doing the work, or any tips or tricks that might help.

I'll have a 1/10hp transfer pump and hoses, along with a 5-gallon bucket for capturing/ reusing the glycol. I'm assuming I'll need some additional glycol to replace the air. I have no idea what type is in there now, but think a gallon of propylene glycol should be more than enough.

I'll post a picture of the setup in the morning when I get to work, so you can see how things are plumbed and how I plan to pump the fluid through the system.

Thanks!

 

[Ted_Kaczynski]

Dibs on your stuff.

 

[sdmuleman]

I'd be more inclined to think the tubing is blocked somehow. Seems like you'd have to have quite a lot of air for it to be that bad, and where did the air come from? Sounds like worked fine previously, so what changed - isn't just going to magically fill up with air unless there's something else going on.

 

[jeepyj]

have verified that fluid moves through the pex when a call for heat is made.

Do you have flowmeters on the loops?

.

 

[Cryptictoy]

Mixing valve's get changed ? Depending on how it's plumbed and how long ago system was opened could take a while for bleed out. HAve also seen were the domestic water/boiler fill get's munged up and and boiler get low on water.

 

[MurderYota]

Most systems have a make up water valve with a back flow and a pressure regulator and an expansion tank. If all of those are working correctly all you have to do is open up the system on the return side ( I always installed valves and hose connectors just for this purpose) and bleed the air out of the system.

 

[spaceman]

Thanks, guys - see my responses below.

I'd be more inclined to think the tubing is blocked somehow. Seems like you'd have to have quite a lot of air for it to be that bad, and where did the air come from? Sounds like worked fine previously, so what changed - isn't just going to magically fill up with air unless there's something else going on.

All the zone valves were replaced in the spring - system has not had to work hard until recently. My thought is that all the air was not purged out when the valves were replaced. Also, if the air vent is not working, then the air that collects in the air scoop will not get removed from the system.

Do you have flowmeters on the loops?

Nope, but when I open up a zone that has not been heated, I can use the digital thermometer to confirm that the return fluid is heating up. So basically, +/- 140° fluids coming from boiler, return line heats from 65 to about 120°.

Cryptictoy]Mixing valve's get changed ? Depending on how it's plumbed and how long ago system was opened could take a while for bleed out. HAve also seen were the domestic water/boiler fill get's munged up and and boiler get low on water.

Work was done in the spring. I'm thinking not everything got purged out and if the Air Vent is not working, that could make it worse.

MurderYota] Most systems have a make up water valve with a back flow and a pressure regulator and an expansion tank. If all of those are working correctly all you have to do is open up the system on the return side ( I always installed valves and hose connectors just for this purpose) and bleed the air out of the system.

System has a water valve with backflow, pressure regulator, expansion tank, air scoop and air vent. About 18 months ago, during a separate repair, the plumber forgot to turn the makeup valve back on when he was done. That created the first issue with reduced heating results and air in the system. He came out and purged the lines and it was good to go. Based on that experience, that is why I think I have air in the system again. I have checked all ball valves, etc. and all are set appropriately.



Here is the system - from what I read on the interwebs, purging will require me to make sure all the various shutoff are closed (boiler return, makeup water, boiler bypass, close down the mixing valve and shut all the zones down). Then get the transfer pump plumbed into the boiler drain and a 5-gallon bucket with some glycol in it, and a line from the loop drain to the 5-gallon bucket. Open up a single zone, turn on the transfer pump, and watch the fluids emptying into the bucket until air stops coming out. Turn off pump, switch zones, and repeat.

 

[sdmuleman]

Do you not have air vents on the radiators? Should have vents at the high points on each loop.

 

[spaceman]

Do you not have air vents on the radiators? Should have vents at the high points on each loop.

This is radiant underfloor heating - no radiators. just pex under the subflooring.

 

[mrsammi]

It looks like you're trying to remove air from a system at near it's lowest point; not great. Try running one circuit at a time to get max flow and see if you can push the air into the return system and then through the 'Air Scoop & Vent'. Air will hang out at the highest point in the system and can reduce flow and still 'feel' like it's working. Looking at that picture, there are so many places to trap air.

 

[pvkj454]

My old system had bleed valves at the highest point. It was extremely easy to bleed.

 

[sdmuleman]

This is radiant underfloor heating - no radiators. just pex under the subflooring.

Missed that part, but should still have a high point bleed since that's where the air is going to be.

 

[Cryptictoy]

What works good for a pump is a submersible style that you hook the garden hose to and drop it in the 5 gal bucket. Start with a new 5 gals of glycol and have 2 more 5 gal pails to purge into and swap out when half full. The higher flow pump you have the better.

 

[spaceman]

I am not sure if this will help or not. Mine is a older system, with baseboard heaters and uses water. I had really bad pipe hammering. To the point it sounded like the house was falling down! I bleed the system many times, at the baseboards and the manifolds. A few days it would be better but would always come back. I talked the the HVAC guy at work and he said I had micro bubbles. He recommended that I install one of these. https://www.supplyhouse.com/Spirotherm-VJR100-1-Spirovent-Jr-Air-Eliminator-Threaded-3560000-p.
I have not had a problem since.

that is the same principal as the air scoop and air vent in my system, so I have that covered. I am replacing the air vent just in case it went bad - there is no real way to test them...

 

[spaceman]

Mine also had a air scoop and air vent already installed. I put the Spirovent in after the air scoop and air vent.

Ahh - I understand now. Read up on that a little bit and it looks impressive. For now, I'll keep what I have, but the next time I drain the system for maintenance, I'll figure out where I could put one (Although I don't mind sweating copper, it makes me nervous to work on this system for some reason...).

 

[spaceman]

Spent the day up here, and I think things are working much better now. Last week the place wouldn't warm up much above 60° with the system running all night long. After replacing the air vent, and trying to purge the air out of the system*, The main room is heating up much faster. Remember this is in floor heating, so the general rule of thumb is about one to two degrees per hour of room warmth.

​​​​

*I also learned a lot of couple things along the way.

1. A small transfer pump won't work. Does not generate enough lift to push fluid through the zones. I had to run into fairplay and buy the one remaining half horsepower transfer pump from Ace hardware. That worked much better.

2. If you train the expansion tank air, in order to replace a part, you need to put air back in the expansion tank before you try to purge the system. Otherwise the first gallon and a half of fluids you put into the system will just go into the transfer tank. Lol

3. Even if you think you have everything dialed in, and all of the right valves opened and closed, if you don't manually open the zone valve, when you start pumping fluid through the system, it will build up pressure and trip the pressure valve on the boiler line, throwing coolant out of the system.
3. Several repair people and others on the internet suggested using washing machine hoses, I did that. I think the only issue I have with them Is that they all have restrictive openings on them, to keep the pressure going into the machine low. I really don't know if that mattered or not, but I think next time, I will use regular garden hoses?!?!

 

[MurderYota]

Air shouldn’t be getting into your system all the time. Once you bleed it it should be good unless you have some kind of problem with one of the components.