I posted earlier on a situation where I was getting no water circulation in one of four zones on a retrofit install. The pump is getting voltage and the impeller is spinning. The problem appears to be trapped air but despite purging it again and again the problem will not go away for more than a day or so.

The system is piped as shown below:


The Taco circulators have integral flow check valves and not flow checks as shown above. I feel that may be part of the problem. The problem only occurs in the Zone 1 which services the highest level in the house. If I purge the zone the problem will go away for a day or so then come back. Air seems to build up in the zone. The boiler has a functional air scoop as shown below but that doesn't seem to help. I then installed a Taco HyVent in the highest level of the affected zone. This did not resolve the problem.

When the problem last occurred I isolated the circulator pump by closing the upper and lower flange valves. I then removed only the top flange and the check valve which is installed on the outlet of the pump. I discovered that there was no water in the pump's housing so the impeller was just spinning in air. If you look at the actual installation:



you can see Zone 1 is the first zone on the supply line and I believe accumulated air from all zones and perhaps the boiler as well is getting trapped in the pipe below the circulator.

When the circulator is off the one way Taco integral flow check valve located above the pump does not allow water from the zone pipes above to flow back into the pump housing. When enough air accumulates the pump impeller is left high and dry.

To test this theory I temporarily removed the flow check valve and reattached the upper flange. I did not purge the system. Sure enough water flowed back into the pump housing and water was able to circulate again.

The problem is now how to fix this permanently.

Does anyone have any ideas or perhaps another theory as to why this problem is occurring?

 

Water should not be "flowing back" in a hot water system. The system should be full of water.

What is the pressure of your system, cold and hot? How many floors do you have above the boiler? You may be drawing a vacuum on the top floor?
Doug

 

I would place an air separator and vent in the manifold between the zone pumps and the pri/sec T's. The scoop and vent on the seconday return isn't really needed.

Is there an air vent or a place for an air vent on the boiler itself? If so one can also be added there. This is optional but if the boiler has a location for it, can only help to install it.

Al.

 

Chuck the internal check valve & install a separate flow check.

 

Less... you built that? nice touch painting the pipes... something I would do... now if you got out the Dremel and polished up the copper ... and gave it a shot of clear high temp lacquer... whellll, then you'd be as crazy as me... yer close, but not quite there!

Here's how I understand Less's theory...

An air pocket forms under the IFC in the circulator... around the impeller. IFC won't allow air past ... impeller can't pump if there's no water in the chamber... just sits and spins...

If this is really what's happening, then it's a very good argument for not installing an IFC pump in that position.

Also makes me wonder why there isn't a tiny hole in the check valve intended to let air bleed past... you know, like a car thermostat... maybe there is? maybe it's blocked? never looked at one that closely.

Doug, I don't think he really meant 'flowing back' ... it was just the way he described the problem... what he meant was that the air can't 'flow forward', leaving the impeller beached.

Al, why is the scoop and vent not needed?

I doubt there's any air in the boiler.

I'm goin' with Grady on this one.

Grady, are you talking about the 'disc' type of check to replace the spring loaded one in the circ? I'm guessing that the air bubbles would be able to lift the disc and fart past the check valve... you thinking that too? OR, if the flow check were installed a few feet above the pump, that whole pipe would have to fill with air before the impeller was dry. You might even could put a tee with an air vent directly ahead of the new check valve.

I think the air that's collecting is coming from repeated attempts at purging the air from the zone ... adding as much air in the fresh water as you are taking out ... the supply manifold area is probably the lowest pressure point in the system, and it sorta makes sense that's where the air will collect.

 

Less... looking at the pic some more, it does beg the question... just how DO you get in there to change out a circ? Stand on the boiler? Scaffolding? Is it as far back as it looks?

Sorry, but hadda ask.

 

The problem isn't air being returned from the load. It is air being fed to the zone pumps. As long as there is a separator/vent on the secondary feed prior to the zone pumps, the scoop on the secondary return pipe is redundant.

The issue is that air is collecting in the up-pipe of the first zone in line. One could drill a small hole (3/32") in the check valve (IFC) to allow it to bleed through. Or, vent the air before it gets to the pump/IFC.

Checking the piping diagrams in the Burnham Alpine and Muchkin I&O manuals. They show the air vent setup on the feed to the zone pumps.

I mention the boiler air vent as some have a location for one. If it's there it makes sense to use it. I searched Lessismore's other posts to see if I could find out which boiler he ended up using. But couldn't find anything.


As far as what type of air vent to use between the pri/sec T's and the zone pumps. An air scoop should have 18" of straight pipe prior to it. Not sure if there is enough room for one. A TACO VorTech or 4900 Series may be a better choice.

Note that the air is coming from the boiler. As the water is heated it releases air, which is why the air vent on the secondary return isn't a good location.

Al.

 

I see what yer sayin' Al...

Howsomever, this problem will probably go away once enough of the air is removed from the system, at which time the scoop and vent on the return side would 'do the job'. The only reason it's not doing the job now is because the air is trapped. If the air were able to move through the system, it would work fine. This is a transient ... start up issue. Which I don't feel warrants a lot of rework.

It's very possible that if there were a vent on the boiler itself, this problem wouldn't exist. If there is a tapping on the boiler for a vent, try that first. The air just wouldn't get as far as the manifold. Probably what's happening is that the air is collecting in the top of the boiler when it's OFF, after a heat call. That air is 'floating' up and out the supply pipe, and collecting at the first high spot it finds. It appears as though everything is 'uphill' from the boiler to the supply manifold.

One possible problem that could arise with a vent in the location you propose... it's possible that the vent could take a 'gulp' of air everytime a pump starts. How much of a gulp (if any) would depend on the pressure drop between the pump and the PONPC ... I do realize it won't be much... chance of it happening, probably slim to none, but there is some chance... why design chance into a system?

LESS work IS MORE better. Cutting into a copper pipe and adding a new check valve is WAY easier and better than re-doing all that purty black pipe ...

 

Doug,
You're right I only allowed this as a test due to this specific problem. The system should be full of water but air is being trapped under the IFC valve in the circ pump.

My house is a split level so there are 2 1/2 floors above the boiler. The pressure of the system is 15 psi.

 

Al,
It would be very, very difficult to repipe the system now. That 1 1/2 inch black pipe is brutal to work with.

As for an air vent on the boiler here are the Biasi B10 tappings:
Front:


Rear:


Of the two top tappings on the rear, one is used for the aquastat and the other is used for the PRV. I suppose I could put a tee before the PRV and install an air vent there.

 

I think this is going to be the best fix. I can install a Taco SwetChek in a horizontal section of pipe above the circ pump.

Will the SwetChek allow the air to pass (unlike the IFC valve)?

 

Trooper,
Yes I built it. Polishing and lacquering the copper is of course insane but I like the idea! I thought I was nuts to paint the pipe but it's good to know there's someone else even crazier out there. Good plumbing is artwork to me. It should be finished like good woodwork.

That's exactly right as far as I can tell. I had a nagging feeling the IFC valves were going to give me problems. I wouldn't reccomend them to anyone.

There's no bleed hole in the valve but that's a great idea. You should submit that to Taco. I may give that a try.

If I do install the check valve I'll also install a tee with a bleeder. Will a Taco SwetChek allow air to pass?

I think that's exactly what's happening.

 

Yea, as you can see it's a very small room (closet size) and I had to go verticle to fit everything. A small step ladder is required to get to the circs. I didn't plan on servicing them a lot.

 

Without a dedicated tapping for a boiler vent I wouldn't go through the trouble of adding one (to the boiler). Some of the boilers have a tapping designed for an air vent. It is placed in a pocket at the top of the interior, in which air will collect and can then be vented.

I figured it wouldn't be easy to place an air separator between the pri/sec T's and the zone circ's. I didn't see a union or such to be able to unthread the pieces.
To me it is that this is the proper solution to the air lock.

Although if it were my system I would be very tempted to drill the small hole in the check valve. Quick and easy, only side affect will be a slight flow of water through that zone.

Al.

 

I don't think so... but even if you do get air behind it, the chances that enough air will collect to fill the entire pipe all the way down to the circ are probably very slim. Adding an autovent on a tee ahead of the flo-check is probably a good idea... maybe not needed though.