Insufficient flow in hydronic system
Last Post 19 Oct 2015 07:48 AM by chingo. 35 Replies.
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chingoUser is Offline
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12 Oct 2015 08:43 AM
primary panel
ronmarUser is Offline
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12 Oct 2015 05:04 PM
Ok, let me see if I am visualizing the flow correctly from your pics.

1. The primary pump panel is drawing it's fluid out of the bottom of the boiler, across under the three zone panel, UP thru the primary pump. Then thru the air sep and back up and across to the top port on the boiler?(that is what the pump orientation tells me, read more below)

2. The three zone panel draws it's water off the primary loop comming from the bottom of the boiler. The water flows up thru the mixing valve where it can mix with return loop water, then up thru the commanded pumps. Looks like the left most pump feeds the manifold below the panel, and the other two go off to feed the other thw zone manifolds above?

Well your problem could lie with the thermal reg valve. If it were in the wrong way around,IE: hot feeding where the cold should be and vis versa, that would cause your problem. For safety, these things are designed to shut down the flow if they cannot get enough cold water to make their commanded mix temp. Hot trying to enter the cold side would probably cause it to limit flow drastically...

Having been doing a LOT of research lately I have not seen a boiler outlet at the Bottom. Since your air sep is away from and lower than the boiler, and the flow is down thru the boiler, how do you keep the boiler from accumulating air(very bad)?

Now the Watts documentation shows the flow thru the primary panel from left to right(down thru the pump) which would be appropriate for an upward flow thru the boiler, the way your system appears to be plummed. The reason I am saying the flow is the opposite direction, is the way the pump on the primary panel is shown in the above pic. According to Grundfos, The 15-58 pump, with the motor end facing you and the control box on the left, has an upward flow... Is that primary pump installed correctly? According to Watts it should be pumping down, with fluid exiting the primary panel to the right. Their pics show the pump control box on the right side of the pump motor which would support the left to right panel flow specified by Watts and would be more appropriate IMO based on the way your boiler is plummed in.

I don't know if that would cause your problem though, as the primary is there to maintain hot flow past the inlet to the mixer and pumps, and it would probably do that flowing either way, unless there is some type of flow diversion in the zone panel where the zone supply and returns are plummed into the main line across the bottom(restricted orifice between the supply and return "t" fittings). If this is the case, then reverse flow could cause the mixer to be fed incorrectly with supply and return water and be causing your issue...

IF this were my system, I would relocate that boiiler down a few feet and run the boiler outlet pipe across BELOW the panels to the primary panel inlet. This would put the air sep at a high point in the primary loop, a much more appropriate location IMO.
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12 Oct 2015 05:25 PM
mixing valve installed wrong is a great point.

but I really don't think air in the boiler is causing any issues for him, and that air sep should remove air, wherever it is.
Rockport Mechanical<br>RockportMechanical.com
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12 Oct 2015 05:46 PM
The air sep should take the air out. but if the primary flow indicated in the pic(backwards), any air that makes it to the boiler won't be able to leave out the bottom... Might cause problems later...

The more I think about it, I think his primary pump is in backwards and reversed flow thru the zone panel IS causing the poerational flow problem. The thermal reg valve is getting confused and limiting flow when hot water is passed thru the system. With his purge rig setup and circulating cold water the thermal reg probably wouldn't limit flow, so he gets better flows with the purge rig attached...
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13 Oct 2015 07:17 AM
I totally agree with you that mixing valve orientation could be the problem. If the cold leg is not pulling from the return appropriately that sounds like a very likely suspect.

But I do think you're barking up the wrong tree with air sep and primary loop direction issues. The air sep will starve the fluid of oxygen and remove bubbles even if the boiler is higher. And there are many boilers with bottom tappings for supply/return where the boiler is the high point. I'd leave all that alone and focus on the 3 way valve... nothing in the boiler loop should affect flow through the zones at all since he's hydraulically separated with the closely spaced tees.
Rockport Mechanical<br>RockportMechanical.com
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13 Oct 2015 08:40 AM
To clarify pictures flow is from left to right. The UPS 15-58 on the zones has the flow arrow that is embossed on the housing pointing up toward check valve. hence flow is from bottom of pump out of top. The Primary circ. pump has the arrow pointing down. hence flow is from top of pump out of bottom toward zone pumps. Boiler is fed from bottom and out of top. I don't know why the orientation of pumps is same even though flow is different. Watts must of had them built specially for them to make the panels more uniform (anyone know)???
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13 Oct 2015 11:08 AM
You can probably rotate the motor housing/control box on the pump to make the pump more adaptable for different instalations.

Ok then, since flow is correct, check your thermal reg valve...

If your thermal reg valve is bad, since you are using the same temp for all your zones, you could do away with the thermal reg valve all together and set the boiler aquastat to your system op temp... Just make an elbow with the same type unions the thermal reg valve uses to connect the line running up into the thermal reg over to the pipe feeding the zone pumps. Make a caped union and cap the return line where it branches over and into the top of the thermal reg valve. The system would draw hot water from the main line and return all it's water back into the main line to the boiler... This has the advantage of not having to worry if the valve is working properly

It appears as if you are not using the primary loop water anywhere else(to heat indirect domestic hot water tank, or feed higher temp radiator)? This system could have probably been done simpler as the main reason for the primary/secondary loop is if you are using a boiler that is sensetive to thermal shock(cast iron), or need high and low temp supplies. That electric boiler(thrmolec?) shouldn't have a problem dealing with temp swings. So your system could have skipped the primary loop altogether, flowing from boiler outlet, past relief valve, air sep/exp tank directly to zone pumps thru their check valves and onto the zones. Then the zone return plummed directly back to the bottom of the boiler...
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14 Oct 2015 09:18 AM
Since this system is isolated. Uses Axiiom MF200 for pres/fill purposes. COULD the inlet pres. be the issue. House is a bungalow pumps in bsmt. My system is set to 12psi. The Mixing valve that is in the system i a series Watts 1170-M2 it specs are as follows. Minimum supply pressure (Static): 30psi Inlet Temp. hot inlet 120F-200F cold inlet 40F-85F Hot Water Inlet to Outlet Diff Temp. 5F Temp. Out Field Range 90F-160F adjustable +/-3F Max. Temp. 200F Max. Pres. 150psi Max. Pres Diff Between Hot and Cold Water Supplies 25%
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14 Oct 2015 09:21 AM
In process of eliminating 1170, but was going to boost pres before inlet to 35psi and run. See if it will make a difference.
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14 Oct 2015 11:03 AM
CAUTION here, the system pressure rises when the boiler kicks in and adds heat/fluid expands. The system relief valve should limit max system pressure to around 30 PSI, so if you bump the pressure up high, the safety will just dump fluid when the boiler kicks in and the fluid heats and expands... IF your boiler is set above 120F, this vented water could hurt! If the safety isn't working properly, you could blow up lines, manifolds or the boiler vessel itself...

Pressure should not be an issue anyway. This is a closed system, regardless of what you set the SYSTEM pressure at with your makup pump, that pressure is basically felt the same on all three ports. The circulating pumps provide the differential pressure that causes fluid to flow thru the mixer. System pressure could be 12 PSI or could be 30 PSI, the valve is still only going to see the differential pressure created by the zone pump...

The valve should have some letters cast into it's body at each port. The ports on either side of the control should read "H" and "C" for hot and cold, with the line opposite the control marked with a "M" for mix. For your installation, the port marked "H" should be pointing down toward the main line(hot water in), the port marked "C" should be up, with it's pipe running up and right to connect over to the return line(cold in). Of course the "M" mix line will connect over to the zone pump inlets.

What is your boiler temperature set at anyway?

What temp are you trying to get out of the mixer?
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14 Oct 2015 12:58 PM
...regardless of what you set the SYSTEM pressure at with your makup pump, that pressure is basically felt the same on all three ports.The circulating pumps provide the differential pressure that causes fluid to flow thru the mixer.
Unless, due to low static pressure, the pump cavitates. Then it produces less differential pressure.

The 1170 is quite restrictive (eg, 5 psi/12' at 5 gpm).
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14 Oct 2015 02:51 PM
Yep, It would have to be pretty low/really restricted on the inlet though. I would hope Watts engineered this correctly for the zone pumps(possibly all 3 at once), to function with the 1170 in their inlet path...

I think he should bypass the thermal reg alltogether. That would definitely solve any restriction issues I don't really see the need in his application as he dosn't appear to be using hot water from this system anywhere else and is using the same temp to the three zones. He could set the boiler to maintain his system op temp...  The boiler he is using may have outdoor reset capability, if so, pulling the thermal reg would allow him to make use of that feature also...
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14 Oct 2015 05:49 PM
The 1170 is installed in its correct configuration. M to input to pumps C coming back from the loops H coming from boiler My system temp is set to 110F Relief valve was shipped with boiler.
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14 Oct 2015 05:52 PM
looking for approx 100 - 105F for system. but 110 would do just fine so don't really need 1170.
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16 Oct 2015 10:03 PM
Posted By chingo on 14 Oct 2015 05:52 PM
looking for approx 100 - 105F for system. but 110 would do just fine so don't really need 1170.


I don't think you need it for your systrem. The boiler should be able to be adjusted down to 100F With the reg valve out, you could add an outside temp sensor to your boiler and take advantage of outdoor reset to boost the system temp/floor temp a little automatically as it gets colder outside. The little boost in system temp helps the system keep up with the added heat loss in colder weather.
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19 Oct 2015 07:48 AM
Thankyou everyone for your input. Took out mixing valve and cleaned filters. Replaced and purged, then repeated. System flow greatly improved. This was the problem all along. Still not getting what i had calculated for flow. But house will run fine with way it is now. I am now looking for a less restrictive mixing valve OR a way to eliminate as stated above. Hopefully this adjustment will help improve performance and meet my calculations. Again thanks to all for your help Neil :-}
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