Puzzling Flow Switch Behavior

JHMartin

Hello,
Sorry for so many questions, but today I found another puzzle, further confirming this may be a snake-bit system. I'm back on Boiler #1, a single loop system where the circulator pump runs all the time. Here is what the flow switch is doing:
No zones calling--Open
First zone (closest to the boiler) calling--Closed
The other 5 zones calling but not the first zone--Open
Then there is this tag (see pic) which may or may not be applicable. I would appreciate your thoughts and advice, as I would really like to get this working as it should.
Thanks,
Jay

mattmia2

if several other zones are calling you should get the same or more flow than the zone nearest the boiler. i'm guessing they aren't flowing or are barely flowing because they are air bound

JHMartin

mattmia2 said:

if several other zones are calling you should get the same or more flow than the zone nearest the boiler. i'm guessing they aren't flowing or are barely flowing because they are air bound

I recently installed a by-pass around the pressure reducing valve so that I am able to purge air at good pressure, I got all sorts of black water, sediment, and air out of the system. I opened the closest valve and kept water running until no more air came out. Then I closed it and moved to the next closest valve. I would estimate maybe 4-5 minutes per zone. Plus, each zone's radiators get (somewhat) hot when they do open. So, I'm getting some flow through each zone. Finally, how can 5 partially, air-bound zones still not equal the flow of that one closest zone? I am not at all trying to be argumentative and hope it's not coming across that way. I'm just frustrated by all the effort I've put into this only to have it still operating so poorly.
Thank you for your input and I'm more than willing to do another purge,
Jay

Mustangman

Interesting, Let me get this right. If you turn the stat up, the corresponding zone should run? So, zone 1 works alone. If you turn the stat down, none of the other zones will operate nor do they close the flow switch. So when you have the thermostat turned up on zone 3, does a circulator come on or a zone valve open, if you have ZVs. The question is, why. I need to know if the circ runs on a call for heat on one of the 5 zones that don't operate. Its hard to diagnose with out knowing how its wired. What circuit is broken by the flow switch? This may not be a flow switch problem.

JHMartin

Mustangman said:

...If you turn the stat up, the corresponding zone should run?

Yes. This boiler is controlled by 6 stats which in turn control 7 zone valves. One stat controls two zone valves.

Mustangman said:

...If you turn the stat down, none of the other zones will operate nor do they close the flow switch.

If I turn the first zone stat down to where it is not calling for heat, no other stat or combination of stats calling for heat will close the flow switch.

Mustangman said:

So when you have the thermostat turned up on zone 3, does a circulator come on or a zone valve open...

Both, that zone valve opens; the circulator pump runs all the time, whenever the boiler is powered on, whether or not there is a call for heat.

Mustangman said:

...What circuit is broken by the flow switch?...

I'm not sure I understand your question. The only individual zone capable of closing the flow switch is the zone closest to the boiler.
Thanks,
Jay

Jamie Hall

Something is fishy. This is clearly a flow problem -- the flow switch is closing properly when it senses enough flow. Either the other five zones do not flow enough, even combined, to trip it -- which seems unlikely -- or could it not be in the flow path to those other zones?

I think I need a complete schematic of the piping.

JHMartin

Hi,
Okay, did another purge and a deep dive into how the zones are piped. I found the closest zone has its own return, if you will, a shortcut back to the boiler. The water for each of the other zones has to circumnavigate 1/2 the building. (Boiler #2 services the other half.) I am concluding that either the 1/8 horse Taco is too weak to produce enough water movement for all but the short route, or the flow switch paddle has such a small surface area that only zone 1's flow rate can move it far enough to close the switch.
I plan to inspect the paddle tomorrow, but am unsure what to take away from that. If the paddle is obviously damaged, I will replace the unit. But if it is intact, I won't know if it is the wrong paddle and has always worked like this of if it's the pump that should be replaced with something more powerful. Thoughts?
Thanks,
Jay

Jamie Hall

It is possible that it is a flow problem in the other zones -- the ones which go around the building. Unless they are each very much smaller than the one which does work, and the total of the four of them is significantly smaller, it's not the flow switch. Nor is it likely to be the pump, unless those zones don't provide enough heat.

I'm rather afraid that you are looking at the wrong problem. True, the immediate symptom is that the flow switch isn't activating -- but don't shoot the messenger. The problem is why isn't there enough flow?

EdTheHeaterMan

On what pipe is the flow switch located? A bypass? A supply that is common to all zones? A return that is common to all the zones? The return you mentioned, that is only on the closest zone?

Have you determined what gets turned Off or On when the flow switch is measuring flow and when it is not measuring flow?

I seem to recall that this is a reverse return system with all the main lines above the Drop Ceiling.

Also, in the diagram you posted showing the boiler piping, is that "closest zone" piping with the "special return" the way it is on the plans you have? That might tell us if that was a redesign because of the faulty original design.

Intplm.

@JHMartin

First make sure all of your zones.....all of them, are purged.
When you say you will be checking the paddle? That's the next step.
Those paddles have had a tendency in my experience to pit or even disappear and lose their performance.
If it is damaged/pitted do change the paddle.
I found that the paddles are very thin. They look like they are made of stainless steel and should hold up better but that may not be the case.
I became so fed up with them failing that I fabricated new paddles with plastic, and screwed them on the control arm in place of the metal paddle.
( I think I used Lexan ). Doing that stopped the problems.

JHMartin

EdTheHeaterMan said:

On what pipe is the flow switch located?...

It is on the supply pipe coming out of the boiler, the supply common to all zones.

EdTheHeaterMan said:

The return you mentioned, that is only on the closest zone?

Yes, I'm attaching a close up of that zone. The main, long return starts on the back end of the next baseboard, proceeds to each baseboard, and then loops back to the boiler. For some unknown reason, the first zone taps into that return just before it heads back into the basement.

EdTheHeaterMan said:

Have you determined what gets turned Off or On when the flow switch is measuring flow and when it is not measuring flow?

The flow switch goes to the ignition module. Is that what you were asking.

EdTheHeaterMan said:

I seem to recall that this is a reverse return system with all the main lines above the Drop Ceiling.

Yes, good memory!

EdTheHeaterMan said:

Also, in the diagram you posted showing the boiler piping, is that "closest zone" piping with the "special return" the way it is on the plans you have? That might tell us if that was a redesign because of the faulty original design.

Correct and thanks so much. I'd be going crazy without the help.
Jay

JHMartin

Jamie Hall said:

...I'm rather afraid that you are looking at the wrong problem...

I don't doubt that for a minute and am happy to be schooled.

EBEBRATT-Ed

The flow switch (assuming the paddle & switch are good) needs a minimum flow to work. I think those switches are supposed to be in a horizontal pipe with the control on top (can't remember).

Also the velocity through the pipe matters. If the pipe is oversized where the flow switch is (not likley) it may not work.

Lastly sometimes you have to trim the paddle if it is getting hung up in the tee. This could cause it to work in a zone with a higher flow and not work in a zone with lower flow. Also the paddle could be gunked up.

They can be finicky

Intplm.

EBEBRATT-Ed said:

The flow switch (assuming the paddle & switch are good) needs a minimum flow to work. I think those switches are supposed to be in a horizontal pipe with the control on top (can't remember).

Also the velocity through the pipe matters. If the pipe is oversized where the flow switch is (not likley) it may not work.

Lastly sometimes you have to trim the paddle if it is getting hung up in the tee. This could cause it to work in a zone with a higher flow and not work in a zone with lower flow. Also the paddle could be gunked up.

They can be finicky

This is a very good point. Flow must be established, so a purged system is vital.

Installation in the horizontal position is the only way I have seen or installed them so I believe that horizontal install is a must.

These units come with different lengths of paddles so the installer can choose the correct length to fill the diameter of the pipe so that the paddle can move freely while getting the most of the volume of flow.

A piece of the paddle can flake off from a main portion of the paddle while still being attached, intermittently scraping the inside diameter of the pipe contributing to a false reading. ( Sort of when you see a vehicle driving down the road with a fender hanging off a bit, scraping the road.)

Jamie Hall

All very good points, folks -- but we still haven't come up with a solution to why the switch works more or less reliably on one zone, and not on any other. I really really want to know whether there is flow in those other zones... and if not, why not.

EBEBRATT-Ed

This may help with troubleshooting

mattmia2

There is also the question of why a flow switch instead of an end switch on the zone valves or another contact on the relays for the circulators depending on how this is zoned.

JHMartin

Hi,
I made an oversized paddle out of Lexan as per @Intplm. It "works" in that the flow switch closes now with just the circulator pump running. What I don't yet know is if my paddle will overly restrict the flow of hot water. I am also unsure how to best test for that. Obviously if the baseboards won't get hot, but would putting an amp meter on the Taco give me an idea of too much head pressure? Feeling some progress even though I may just be masking the true problem.
Thanks all,
Jay

mattmia2

If you just want it to call for heat whenever the circulator is running why not just wire a relay with a 120v coil to the power to the circulator?

JHMartin

mattmia2 said:

If you just want it to call for heat whenever the circulator is running why not just wire a relay with a 120v coil to the power to the circulator?

Good point. I also thought about just jumping the flow switch, but figured there was some valid safety concern for having a working flow switch in the first place. Boiler #2 has a primary and secondary circuit with one pump running continuously that keeps what I call the halo, the circuit running around above the drop ceiling, always up to temp. I question the efficiency of the design, but that’s how I found it. If my oversized paddle isn’t too much of a restriction, that is how Boiler #1 will now be working, i.e. an always-on, warm halo.
I’ll test my paddle once it cools off again, starting tomorrow.
Thanks,
Jay

mattmia2

Ideally the boiler would only fire when there is a call for heat somewhere to reduce standby loss. In a moderate sized building with many zones that probably rarely happens.

Keeping the mains in the ceiling hot when there is no call for heat is wasteful but also may be the only thing keeping some of it from freezing.

hot_rod

Use the spec sheet to see how much minimum flow that switch needs. What kind of tee is it threaded into. Best to use a threaded tee, not copper with adapter, as the paddles don't fit copper tube so well.


Occasionally the paddles erode away also and you may need a new stainless paddle.

EdTheHeaterMan

This sounds like a prime candidate for an inexpensive outdoor reset device. Circ. runs constantly on the Halo loop. As the outdoor temperature drops, the boiler is allowed to make hotter water in the loop, as the outdoor temperature increases, the boiler temperature is reduced. (you may need a bypass with a differential pressure valve that will bypass if all zones are closed.)

https://s3.amazonaws.com/s3.supplyhouse.com/manuals/1351070159526/84935_PROD_FILE.pdf

EBEBRATT-Ed

Putting a flow switch into the branch of a threaded tee is tricky. The flow switches are usually 1" so people use a tee with a 1" branch and the paddle will rub or not work at all.

Better to use a tee with a branch tapping larger than 1" and put a bushing in it. Gives the paddle more room to work.

hot_rod

With the Caleffi flow switch the number on the paddle indicates what size pipe it needs to go into. The dimension given if you use a weld outlet for example.

Trim  the end if it bottoms out and binds.

JHMartin

hot_rod said:

...What kind of tee is it threaded into...

It is a 1 1/2 x 1 1/2 x 1 1/4 tee, but I'm confused. Both the documentation and the cover state that model is supposedly 1" NPT. The stainless paddle that was in it was 1/4" longer than the instructions. The Lexan one is another 1/8 longer plus has no tapered shoulders at the top. We seemed to be getting good heat upstairs. So I may just leave it alone for now.
P.S. When researching flow switches I watched you present on YouTube. Thank you for chiming in here.
Jay

Intplm.

Good move fabricating the Lexan. It doesn't fall apart and scrape the inside pipe wall giving the intermittent, confusing readings.
The switch can be bushed down with a 1 1/4" x 1" bushing off the branch of the tee.
The original installer probably didn't have a 1 1/2" x 1 1/2" x 1" tee when it was first put in so they used a bushing.
Glad it's working out.
Nice job.

JHMartin

Jamie Hall said:

...I really really want to know whether there is flow in those other zones... and if not, why not.

I inspected one of the zone valves this morning and found its brass connection really reduces the flow, maybe dropping it down to 1/2" or even 3/8". I should have taken a picture. If that type of zone valve has been used throughout, that could be the cause of those zones being unable to close the flow switch.
Jay

JHMartin

EdTheHeaterMan said:

This sounds like a prime candidate for an inexpensive outdoor reset device. Circ. runs constantly on the Halo loop. As the outdoor temperature drops, the boiler is allowed to make hotter water in the loop, as the outdoor temperature increases, the boiler temperature is reduced. (you may need a bypass with a differential pressure valve that will bypass if all zones are closed.)

https://s3.amazonaws.com/s3.supplyhouse.com/manuals/1351070159526/84935_PROD_FILE.pdf

Being new to all this, I have been trying to first get what's there working. As my confidence builds, I can surely give this serious consideration. I appreciate your suggestion.
Jay

hot_rod

When it comes to valve sizing we use the Cv value. So the zone valve orifice may look reduced, but still flow plenty.

A common 3/4 zone valve will be 7-8 Cv
That means at an 8 gpm flow, there us a 1 psi pressure drop across the valve,  typically you would flow 4-5 gpm in a 3/4 copper tube, so the zone valve should not be a flow restriction 

But always check the Cv number of the valve, there are some applications that use low Cv valve, a 1 Cv for example.