How to automatically vent domestic hot water recirculation loop

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Greenthorn

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Nov 11, 2018
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I'm not a plumber but I carefully installed a recirculation loop and pump and it doesn't leak. However, it didn't work either. I suspected the pump was air-locked, installed a hose bib near the pump to purge air. Success! But every week or two the system fails. I had assumed any air would be removed through continual use of the fixtures. That was wrong. So I get a bucket and purge more air/water through the hose bib and everything works great again for a week or two. My questions to the sage among you are:
1. What specific automatic air vent should I install and in what specific location? (I'm aware the devices themselves are to be oriented vertically)
2. Should I reconfigure the orientation of the pump or anything else to be sure the vent will work?
See photo:
https://www.plumbingforums.com/media/img_6799.653/full
 
I am far from an expert, but I have seen bleeders on some hydronic boiler systems, usually near the circulator pump. I believe they work automatically to bleed air out of those lines.
 
It may not be relevant to the issue but the pipe routing appears strange to me. Perhaps I'm not seeing it correctly.
First off, it appears that there are 2 recirc. lines coming back to the pump. The lines with the green handle valves and check valves. Since the top of the pump appears to go to the cold water inlet on the tank, I assume that's the return of the recirc loop. However, the lower of the 2 Return lines appears to have a check valve with the flow arrow pointed to the right. And on the line above it, it almost looks like someone drew an arrow pointing left. If you do, in fact have 2 return lines for recirc of 2 different areas, do you have balancing valve to help control even distribution of the recirc water?

I believe an automatic air release valve should be located at the top of the recirc. loop, somewhere in the upper level of the house. In fact, even at the pump location, a potential air trap was created by coming up from the pump, over to the right and then back down. Not the best arrangement.

Why 2 return lines?
 
At least purge each return independently. Not gonna do right on one line. Need a balancing valve to keep flow going evenly. Or something else is allowing air to enter your system. But purge both lines by their selves then turn both on
 
Diehard said:
It may not be relevant to the issue but the pipe routing appears strange to me. Perhaps I'm not seeing it correctly.
First off, it appears that there are 2 recirc. lines coming back to the pump. The lines with the green handle valves and check valves. Since the top of the pump appears to go to the cold water inlet on the tank, I assume that's the return of the recirc loop. However, the lower of the 2 Return lines appears to have a check valve with the flow arrow pointed to the right. And on the line above it, it almost looks like someone drew an arrow pointing left. If you do, in fact have 2 return lines for recirc of 2 different areas, do you have balancing valve to help control even distribution of the recirc water?

I believe an automatic air release valve should be located at the top of the recirc. loop, somewhere in the upper level of the house. In fact, even at the pump location, a potential air trap was created by coming up from the pump, over to the right and then back down. Not the best arrangement.

Why 2 return lines?
Click to expand...
I don't think any of this is relevant but will serve to explain the whole layout...There are 2 return lines because the heater is located roughly in the middle of the house so I have plumbed a 2 branch system. In fact only one branch is in use for now and the second is just a stub. The valve for the unused branch is closed. The green handles are for globe valves that are for balancing the flow in the branches. Both check valves are oriented toward the pump. Flow from the pump goes into a port in a tank mixer that is dedicated for that purpose. Much of my layout is based on a diagram provided with the Caleffi tank mixer. The mixer has been a godsend in my 4 person household- I have the tank at about 140 degrees and the outgoing temp is 120.

Regarding the air valve, I did talk to an experienced professional plumber and show him the same picture. He suggested inserting a T just below the pump and putting in a vent such as a Watts FV4 there. However, I think air could collect just under the pump even with that addition. That's why I'm considering re-orienting the pump to a horizontal run of pipe and installing the vent along that run just before the pump. I'm hoping someone out there is a guru and can offer definitive advice.

Thank you for your input.
 
Well sounds like you have the recirc system well under control. Picture was a bit blurred for me and I thought I saw an arrow pointing the opposite way. Just making sure.
I'm obviously not the best person to advise you on the cause and fix. But I doubt the airlock is at the pump. I'd speculate that since it's a circulator and not a pressure pump(i.e.-Typically can't lift much of a head of water.), the air lock is in a location causing the circulator to try to lift more water than it's designed to do. I don't know what the shut off head is for that unit but I'd guess it's maybe a 1/25 HP unit with like 16 - 18 foot shut off head.(Won't flow any more due to pressure requirement.) So I would be thinking pocket of air high up in the system since air rises and that's were I'd put an air release valve. But I'm not plumber or an HVAC person. So I'd be quite interested in hearing the final resolution. Realizing of course that it will take weeks for this.

EDIT: Come to think of it, I bet that loop on the discharge side of the pump could trap enough air to cause problems circulating.
 
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EDIT: Come to think of it, I bet that loop on the discharge side of the pump could trap enough air to cause problems circulating.[/QUOTE]

The top horizontal run of the loop is exactly where I thought the vent should go originally but the professional suggested otherwise. I don't fault him if he's wrong- he really just looked at a picture on my phone for about 10 seconds and threw out an idea. I may put the vent at the high point first and see if that solves the problem. I think you're pointing me in the right direction because there is no sound of cavitation at the pump. I remember hearing obvious cavitation sounds when I first connected everything, but haven't heard them since. I will eventually get it figured out and will post again about the solution.
 
You really don’t need to spend that money. Once air is properly evacuated then you will never “build “air again. City might introduce some but under normal situation air can’t just jump into pressurized water line.
 
Jamesplumbing06 said:
You really don’t need to spend that money. Once air is properly evacuated then you will never “build “air again. City might introduce some but under normal situation air can’t just jump into pressurized water line.
Click to expand...
The thing is, something is causing the hot water to quit recirculating. I think it is air near the pump because, if I purge a bunch of water through the hose bib near the pump, the recirculation resumes. This happens every week or two, which is the point of the original post. I know that air is being released from water when it is heated because when I fill the bath with hot water there is a fair amount of air in the form of very small bubbles. It takes a minute or two till the bathwater is clear and the bubbles have reached the surface. I have not seen any evidence that the pump is doing anything other than what it should be. I even have it plugged into a Kill-a-Watt, which shows that it is periodically pulling about 5 Watts of power. Jamesplumbing, what besides air bubbles generated in the water heater do you think might be causing the system to fail periodically?
 
Pump impeller bad and need new pump. But the whole 2 returns coming in kinda gets my brain hurting. I always have made a true loop single line. unless you have a solinode system to give flow to one side or the other. It’s hard to get perfect parallel system to draw perfect. Globe valves will work till heat takes over and stay higher. And forces the other line to circ more. And cause a current. Even when the hotter water cools the “current “ is created and stays. In my head. But I ain’t the expert on double return lines. You impeller is cavitating from the steam created. Might check temp. But cavitation usually is caused from bad prop.
 
im no expert on recirc set up
but I would try keeping it simple by only having the pump,hose bib and check valve.and you need a cross over tee in tha farthest fixture for that comfort series pump
 
ExtraMilePlumbing said:
im no expert on recirc set up
but I would try keeping it simple by only having the pump,hose bib and check valve.and you need a cross over tee in tha farthest fixture for that comfort series pump
Click to expand...
Why do you say this? Are you saying this pump series, on an added pipe recirc system, may be contributing to the air lock problem?
I see the comfort series is a very low head and flow circulator, that certainly would make it more susceptible to air lock problems.
 
@Greenthorn...Just curious. What size pump do you have? GPM vs. discharge head.
What's stopping you from putting an automatic air release in some of your high spots, which are subject to trapping air? Of course, the reason you should have to, is the real question.
Are you sure you're purging all the air out of the complete system when you do it? In other words, causing the water to flow through the entire loop, throughout the house, by shutting that top ball valve feeding back into the cold water. If you leave that valve open, it of course would not be forcing water through the entire system but just from the cold water line to that draw-off faucet. Maybe the system was never properly purged from day one. ????
Just trying to touch all bases.;)
 
I will say. I haven’t seen an air gap installed since I was a kid. And even then it’s a vacuum breaker that allows water to be drained from a system. And also allow air to rise into a non flowing pipe to be trapped forever. Please send me a link to a plumbing fitting that knows the difference between air and water and automatically discharges air only. That will blow my mind. And it should forever be a code to install in every house.
 
Wait wait wait. Has anyone else noticed the cross over on top of heater hot to cold. Why?
 
I just now sat down and studied your setup. Wow. Don’t be surprised If a pro wants all that tore out. That’s just insanity. The temp sensor should be tied in just before cold line. That cross over to allow you turn up temp and only use certain temp to elongate your hot usage. Those are trouble waiting to happen. Use your faucet to adjust temp. I would simplify that. 1 cold coming out 1 hot make a total loop tie in temp sensor just before tying into cold. Check valve on return and on cold. Done. That mess is just a mess. I am out. Maybe someone else can help with that. But I like easy and simple Maintenace. Seen some massive industrial boilers not have that many connections and flow patterns.
I just mean I will be more harm than good. Don’t take me backing personal. Just never seen a nightmare like that. Easiest for me to rip out and do what know works flawless
 
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Lol you don’t service those do you? They go out every 3-4 years cost a couple hundred. And pointless unless this is commercial ? Every faucet has a cold side. That’s just another financial burden for nothing gained.
 
The reason I say I like it is because it looks like something that would much better in place of my tempering valve, on my oil fired boiler with a tankless water heater built into it. My wife is always complaining about the water being too hot(at the kitchen sink) or not hot enough. It has a big temperature range an d does a lousy job of controlling the temperature of the hot water. But I suppose if I had a tank type water heater, I wouldn't have such a temperature swing.
 
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