How do I avoid trapping air in return line when refilling boiler

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Old 11-02-13, 06:47 PM
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How do I avoid trapping air in return line when refilling boiler

I have an oil-fired boiler and with 3 Taco 571 zone valves and 1 Taco 007 pump. There are 2 heat zones and 1 zone valve controlling a Super Stor DHW indirect holding tank. The 007 pump is located on the return line just downstream from the return manifold (close to the boiler).
After 22 years, the zone valve to the Super Stor is going bad. Definitely not the motor - I can remove the motor/head completely and that 571 will still allow flow if a heat zone is on. The only way to stop this flow is use the SS shutoff at the drain. Might be a spring, or something cracked inside the valve, but I definitely need to open it up and try to swap out the hardware.
There are no isolation shutoffs at the zone valves, so given that I have to drain the boiler, I'm looking at the refill job and having a problem figuring out how to avoid getting air trapped in the return side of the piping. I know how to bleed zone-by-zone, and have done that job in the past, but the boiler was basically full at the time. The system has the standard auto-fill valve, which I know will fill the boiler and (one zone at a time) push water up the boiler supply pipe, through the zone valve, downstream piping, and eventually out the zone drain. So that takes care of getting all of the air out, EXCEPT that there's a return line from the Super Stor back to the boiler and also the return line back to the boiler from the common return manifold (downstream from the zone drains).
I don't see any possible way for these 2 return lines to get air purged and water in during the purging of the zones, because those sections of piping become isolated from the purge water flow. And I'm expecting that when I open up the system, all of this trapped air will flow throughout the entire system and result in a big full system air purge effort (or maybe even more than one). I'm trying to figure out how to avoid that and get those return lines purged along with the rest of the system.
I'm thinking the only way to get these lines purged would be to use the fill valve pressure to first push water in reverse flow up the return piping until it flows out the zone drains. After doing that, I would close the zone valve shutoffs and perform the regular forward flowing zone fills. But I'm not sure about the pump. The 007 pump doesn't have the IFC, so I'm thinking it should allow water to flow through it in a reverse direction, but can't find anything to confirm that (with no damage to the pump).
Has anyone been through a similar thing in the past? If so, is my idea above basically correct, or am I missing something about this whole boiler refill process? Maybe the air can't be pushed out of the return lines like I'm thinking, and a follow-up full purge will always be necessary.
Thanks in advance for any insight and advice on this.
 
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Old 11-02-13, 07:38 PM
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It's always difficult with no valves. If you have to drain the system why not put some in for the next time. If your main concern is the pump then the answer is it will not hurt the pump and the water will Flo in both directions. If that will solve your problem I don't know. The way air gets into a system is when fresh water is introduced. The more water you let in the more air you will have..
 
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Old 11-02-13, 07:50 PM
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After 22 years, the zone valve to the Super Stor is going bad. Definitely not the motor - I can remove the motor/head completely and that 571 will still allow flow if a heat zone is on.
Before you go ripping into the system...

What are you actually observing as the problem?

In the quote above, I'm confused by what you are trying to say. Why does it follow that it is 'definitely not the motor' if the valve opens when you remove the head?

I'm not sure that you understand the way that a Taco zone valve works. When you say 'motor', you know that they don't have what we typically think of as a motor, right?

It's called a motor though, specifically a HEAT MOTOR.

The Taco valves work on the principle of heating and cooling a 'wax' that is trapped inside a 'bellows' that is heated by a heating element around that bellows mechanism. As the wax is heated and cooled it expands and contracts, which opens and closes the valve. It is possible for this type of valve to fail and either NOT CLOSE the valve, or NOT OPEN the valve. It depends on exactly what part has failed IN THE POWERHEAD.

My recommendation is to first replace the power head. I'll buy you a beer if this doesn't fix the problem.

Wait... I take that back. There IS a spring that should push the valve CLOSED when you remove the head, so you may be right...

IF that is what is happening. If the zone valve does not close when you remove the head, then yes, it's probably in the valve body itself...

Carry on, don't mind me. Here's your beer!
 
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Old 11-02-13, 09:00 PM
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It's always difficult with no valves. If you have to drain the system why not put some in for the next time. If your main concern is the pump then the answer is it will not hurt the pump and the water will Flo in both directions. If that will solve your problem I don't know. The way air gets into a system is when fresh water is introduced. The more water you let in the more air you will have..
Thanks for confirming that. I don't know if it will help either, but since it won't hurt the pump, then there's nothing lost by trying it.
 
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Old 11-02-13, 09:38 PM
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.... Wait... I take that back. There IS a spring that should push the valve CLOSED when you remove the head, so you may be right...

IF that is what is happening. If the zone valve does not close when you remove the head, then yes, it's probably in the valve body itself...

Carry on, don't mind me. Here's your beer!
Yep, that's what's happening. I've swapped heads, and even removed the head completely for an extended period of time, but the Super Stor always continues to heat up and approach the 180 BB water temp. I've been using the zone shutoff valve as an on/off switch to stop the flow/overheating until I can get the zone valve fixed. This all started a couple years ago with what I thought was just a minor ghost flow, but it's been getting worse over time. It is odd that the spring strength of the bad valve doesn't seem different from the new replacement valve that I bought, when the nub is pushed down with large pliars. That makes me suspect that maybe the inner rubber gasket that spring pushes up on to stop flow is torn or wearing away. Doesn't really matter though because it has to get fixed regardless of what the problem is.
 
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Old 11-03-13, 04:15 PM
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It is odd that the spring strength of the bad valve doesn't seem different from the new replacement valve that I bought, when the nub is pushed down with large pliars. That makes me suspect that maybe the inner rubber gasket that spring pushes up on to stop flow is torn or wearing away.
So there is still spring pressure?

Yeah, it has to be the stopper then...

Let us know what you find!
 
 

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