Valve remains open when boiler/circulation pump cuts off

MoreCowbell · February 1

Hello – first post to this site …

I have a Crown Aruba boiler set up for radiant heat in the floor (3 zones) and it’s been working fine. However, there’s been a “mystery” ever since I had this place regarding the Zone valve. When the T-stat is kicked up a degree or 2 for a particular zone, the boiler fires up as well as the circulation pump. And the Zone valve (of course) opens during that time (I know because I wired in LED lights for all 3 zones to indicate the open/closed status).

As the system tries to reach the set point temp., it will come on and off several times. Initially, when the system shuts down, the Zone valve stays open! It may not be for several cycles (4-5?) until the Zone valve finally closes.

It’s almost as if the system is saying: “I’m trying to stably reach the set point temp. you chose on the T-stat but until I’m sure I can maintain that, I’m leaving the Zone valve open. Once I’m really sure, I’ll close the valve.”

If this is what’s really happening, where is the ultimate control for opening/closing the valve coming from? 🤔

Any thoughts are appreciated …

109A_5 · February 1

" As the system tries to reach the set point temp., it will come on and off several times. Initially, when the system shuts down, the Zone valve stays open! It may not be for several cycles (4-5?) until the Zone valve finally closes. "

To me your use of the word system is too ambiguous, do you mean the boiler cycles on and off several times while the thermostat and the zone valve are still constantly calling for heat ?

If so I suspect the boiler is actually cycling on the high temperature limit. Since the zone can't dissipate the full capacity of the boiler.

MoreCowbell · February 2

Yes, by "system", I mean the entire unit (burner & pump).

Other than that, the scenario is exactly as I described. As I said - the system cycles on/off several times without closing the valve - until a point is reached when, upon the last shutdown, the Zone valve closes.

Still a little puzzled.

I guess I was hoping to at least hear someone say: "Me, too - my system does the same thing."

Unfortunately, most homeowners would have no easy way to know the state of the Zone valve. That's why I wired in the 3 LED lights because I always wanted to know which zone is getting circulation.

109A_5 · February 2

OK to me the thermostat and zone valves are part of the 'system'. Since they are part of the heating 'system'. Other components of the 'system' are just a subset of the 'system'. Thanks for the clarification.

I still suspect the boiler is actually cycling on the high temperature limit. Since the heating zone can't dissipate the full capacity of the boiler. So the boiler (only) temporarily shuts down on High Limit.

As a test put one of your LED indicator devices across the High Limit switch in the Aquastat. So if the High Limit switch opens the LED turns on.

I would not leave the LED indicator device across the High Limit switch in the Aquastat permanently unless you are 100% confident that a failure of the LED indicator device can't disable the High Limit switch functionality.

Grallert · February 2

Does the thermostat satisfy or does the temperature climb past the set point?

MoreCowbell · February 2

Grallert: The T-stat works fine and no, it never overshoots the set point.

Thank you 109A5. I’m pretty smart but not an HVAC guy. I’m a little confused by your “the boiler is actually cycling on the high temperature limit”. I’m not sure what you mean by “High Limit”.

You mention the “High Limit switch in the Aquastat”. My valve controller is a Honeywell (V80423E1012). As you may hve figured, for my LEDs, I tapped off of the line that gets 24V from the T-stat when it opens the valve. (I always know which valve is open, and when.)

mattmia2 · February 2

sounds like the boiler is somewhat miswired so when the high limit aquastat opens it turns off the burner and the circulator instead of just turning off the burner.

pedmec · February 2

The zone valve is always open on a call for heat until the thermostat is satisfied. The boiler will fire when the zone valve end switch makes. The boiler has a hi-limit that keeps the boiler temperature from getting to high. A normal boiler temperature will be 180 without reset and will shutdown the boiler if the boiler water temperature reaches 180. But that doesn't mean your thermostat is satisfied, so it just keep the boiler temperature from exceeding 180. Because you still haven't satisfied the thermostat your zone valve is still open and the circulator is still running to circulate the boiler water.

109A_5 · February 3

Make and model of your boiler may help. Pictures also.

109A_5 · February 3

Typically with a multi-zone system the thermostat(s) control the zone valve(s). The 'End Switch' (Auxiliary Switch) of all the zone valves are wires in parallel (Red wires). With any thermostat call for heat the zone valve opens and the zone valve's 'End Switch' closes, that activates the Aquastat and the Aquastat then activates the boiler's burner and also activates the circulator. The Aquastat is usually mounted to the boiler so it can monitor the boiler's water temperature.

The Aquastat provides safety and control functionality.

If the Aquastat's High Limit switch opens (boiler's water has reached the high limit temperature) it usually just shuts off the boiler's burner and the circulator continues to run so the hot water in the boiler can continue to heat the calling zone(s).

If the call for heat is still active and the boiler's water temperature drops enough the High Limit switch will close to activate the burner again.

One zone of a multi-zone system is usually just a fraction of the boiler's capacity so the boiler's burner may raise the boiler's water temperature faster than the calling zone can cool the water so the High Limit switch may trip.

You system may be different. Pictures of your system may help to clear up some of the questions.

MoreCowbell · February 3

I appreciate all the more information & thoughts.

• What MEC posted makes perfect sense; sounds right.

• To 9A-5, I mentioned Crown Aruba; the model is DG 150.

In my configuration, the Aquastats are not mounted on the boiler (though it makes sense that they might be). They are mounted directly on the 3 Cu pipes that release hot water back through the (back) wall and into respective zones.

When you say:

“If the Aquastat's High Limit switch opens (boiler's water has reached the high limit temperature) it usually just shuts off the boiler's burner and the circulator continues to run so the hot water in the boiler can continue to heat the calling zone(s).” that also makes sense. However. To my knowledge, I don’t believe the boiler and circ. pump have ever run independently; i.e., rightly or wrongly, I believe they always run concurrently.

This comment:

“One zone of a multi-zone system is usually just a fraction of the boiler's capacity so the boiler's burner may raise the boiler's water temperature faster than the calling zone can cool the water so the High Limit switch may trip.” is interesting may exactly pertain to my system. In fact, of the 3 zones I have, I usually only run 2 of them, and of these 2 – Zone 1 runs 90% of the time based on T-stat settings.

One thing I will do tomorrow morning is this:

I’ll kick up the T-stat a couple degrees and monitor to see whether, when the system shuts down (even with zone valve still open), has the set point been reached? If it hasn’t been reached, then according to this discussion, the Hight Limit may have been invoked. And this might explain the seemingly premature shut down and zone valve remaining open.

Lots of good information here, which I appreciate …

mattmia2 · February 3

can you show us what's inside the front cover? there is usually a built in aquastat that is in a well somewhere on the front of the boiler packaged with the boiler.

109A_5 · February 4

I'm thinking you don't know all the correct names of the components making up your heating system. The "Honeywell (V80423E1012)" are the zone valves. The Red arrow in the image below points to the Aquastat and there is usually only one.

109A_5 · February 4

I suspect your system is like this image (it may not be) and the multiple thermostats and zone valves are inserted at the red arrow.

https://www.velocityboilerworks.com/documents/DG-Manual-Standing-Pilot.pdf

109A_5 · February 4

I believe your system may be like or similar to this, showing only 2 of the 3 thermostats and zone valves for drawing simplicity.

EdTheHeaterMan · February 4

I am with @109A _5 on this one.

Our new member @MoreCowbell has an idea of what is happening but may be assuming something that is not actually happening.

The statements read this way to me:

Call for heat and zone valve LED indicates a call for heat
Zone valve opens (end switch signals boiler control)
Boiler operates both the burner and the circulator pump
Burner and pump both stop for some time but the LED still indicates the call for heat and the open zone valve
The burner and pump come back on for some time and the LED still indicates the valve is open
Burner and pump both stop for some time but the LED still indicates the call for heat and the open zone valve
The burner and pump come back on for some time and the LED still indicates the valve is open.
Steps 4, 5, 6, and 7 continue for several cycles.
Call for heat is satisfied and the LED goes out indicating the valve closes.

This is not how it should work. The circulator pump should not stop while there is still a call for heat and the valve is open. If this is actually happening, then the boiler control is not wired properly or is defective.

I might suggest that the circulator is still operating and that is because those circulator pumps are very quiet and may appear as if they are not operating when they actually are operating. The following is a proper operation for your Aruba Boiler.

Call for heat and zone valve LED indicates a call for heat
Zone valve opens (end switch signals boiler control)
Boiler operates both the burner and the circulator pump
Burner ONLY stop for some time but the LED still indicates the call for heat and the open zone valve
The burner come back on for some time and the LED still indicates the valve is open
Burner ONLY stop for some time but the LED still indicates the call for heat and the open zone valve
The burner comes back on for some time and the LED still indicates the valve is open.
Steps 4, 5, 6, and 7 continue for several cycles.
Call for heat is satisfied and the LED goes out indicating the valve closes.

If you can double check the the circulator is in fact OFF then you need to get something fixed. If the circulator is operating during the burner off cycle, that is normal operation and nothing needs to be fixed. It is operating correctly.

MoreCowbell · February 4

Thanks for all comments since my last post and I have an important update.

Firstly, as to the term "Aquastat", I was unfamiliar with that term when 109A-5 first brought it up. IMHO, "Aquastat" is not a generic term, but seems more like something that derived from a commercial source or a term used within the HVAC profession and it just caught on. There must be a better, more generic name for that controller box that is (in my unit) actually mounted on the end of a 1½” outlet pipe (off a Tee) for heated water to be distributed to the zones. (And when I earlier wrote (referring to the zone valve controllers): “They are mounted directly on the 3 Cu pipes that release hot water back through the (back) wall and into respective zones.” That should have been: “They are mounted directly on the 3 Cu pipes that allow hot water to return from the (back) wall and to return to the boiler”. (I had it backwards.)

Now that I’ve done the test this morning, I now realize that I may have no problem at all. Stay with me.

With T-stat for Zone 1 at 62°, I bumped it up to 64°. The entire system kicked on and, after ~25 minutes on that “climb”, it shut down (T-stat temp. reading 63°). The Zone valve remained open but I noticed something else I had never noticed:

The (German) Grundfos circulation pump remained on !!! This was exactly as posited by MEC and 109A-5 upstream in this thread. (Mechanically, this makes perfect sense in that, even if the boiler shuts down for “safety” reasons, the circ. pump should remain on to distribute heat out into the zone circuit.) So why did I lie and say that the entire system shuts down with the Zone valve remaining open? Because that great German circ. pump is SO QUIET it it’s imperceptible to the ear. So how did I discover it actually continued to run after the boiler shut down? I noticed years ago that I could not – with my ear – tell whether the pump was running (especially when the boiler is fired up). So I wired in (in series) a nifty 0-3 amp ammeter (mounted on a bracket right on what you like call the Aquastat). But I failed to check it when the boiler shut down – MY BAD !!

So in this morning’s test, as Zone 1 was slowly climbing to the set point (64°), the boiler shut down several times while the T-stat temp. reading stayed 63°. At these shut downs, the Zone valve remained open and the circ. pump continued to quietly run, pulling between 0.5a to 0.7a.

When the boiler would shup down, btw, the temp. gauge for the boiler read 165° - which I’m presuming is ideal or certainly acceptable.

Had I checked to see that the circulation pump remained on after the boiler shut down with Zone valve remaining open, I never would have made this post. Again – MY BAD !! However, I learned a lot of good stuff from various contributors - all of which I really appreciated. 😊

Bernie_the_Brewer · February 4

Grundfos is Danish! But I am happy to hear your good news.

109A_5 · February 4

Aquastat I guess is a Honeywell (now Resideo) product name. Another manufacture calls a box with similar functions a Hydrostat. I would encourage you to learn more about your system so if it ever has a problem you can maybe repair it yourself. Every hot water system is kind of unique, but typically uses similar components to build it up. System pictures often greatly help us here to identify things.

If you take the cover off of your Aquastat (turn the system's AC power off first) the part number may be inside (like L8148E), there may be information on the backside of the cover also.

Here is an example below;

https://s3.amazonaws.com/s3.supplyhouse.com/manuals/1350896649620/84126_PROD_FILE.pdf

https://s3.amazonaws.com/s3.supplyhouse.com/manuals/1287574876485/40752_PROD_FILE.pdf

109A_5 · February 4

A more generic name may be a specialized temperature limit and relay or "Combination Limit & Relay".

Seems every trade has specialized names for stuff they deal with every day. Often it is just what the manufacture call them.

EdTheHeaterMan · February 4

Aquastat is a Honeywell trademark name that has been colloquialized to mean immersion temperature controller, hydronic temperature limit control, or boiler high-limit / low-limit controller, including triple high-limit/low-limit, burner, and circulator relay controls.

In the case of your boiler, the generic term for your L8148 Aquastat relay is: immersion temperature high-limit, burner, and circulator relay, to be perfectly technical. That would be different from the L8124, which you might find on a boiler that has a tankless coil and therefore requires a low limit. The generic name for that control would be immersion temperature high-limit, low-limit, burner, and circulator relay, to be perfectly technical.

I kind of like the fact that the trade has decided to use Aquastat to mean all types of immersion temperature controls. That term rules out refrigerant immersion temperature controls, chemical immersion temperature controls, and just about every other temperature control that has nothing to do with hydronic heating.

I also like to think of it the same way I like Royal® brand gelatin dessert, but I still call it Jell-O®, which is a trademark and brand name of a similar product made by an entirely different company.

Again, as @Bernie_the_Brewer stated, I am also happy that you did not have an actual problem, and all is well. I have discussed your exact situation with many of my customers on many occasions, ever since those pumps were made so quiet. Just because you can't hear it does not mean it is not working.

By the way, Just to put your mind at ease, that immersion well temperature sensor that we like to call an Aquastat in the trade, is not supposed to shut off the burner just before it becomes dangerous. If properly adjusted, the burner (Not the entire boiler) will stop making heat long before anything gets anywhere close to dangerous.

ADD ON EDIT:

I remember telling customers that were worried about the thermostat calling for heat and the burner not running the entire time "When the thermostat turns on the circulator pump but the aquastat turns off the burner, that is when you are getting 'FREE HEAT' because you are not paying for FUEL if the burner is not running, but the pump is still sending hot water to your radiators so all the heat is free!."

MoreCowbell · February 4

Thanks again for all the additional posts since I verified my non-problem. Thanks for the etymology regarding the name “Aquastat”. Who knew? I like the Jell-O analogy. And btw, my “Aquastat” is Honeywell, but the label “Aquastat” appears nowhere. I’ve been “inside” is several items.

I not only appreciate all the rich information (in many ways, I learned more than I wanted to know 😁), I appreciated the several diagram posts and document links.

Per 109A-5’s comment – I compiled made a document of this entire thread for future reference.

EdTheHeaterMan · February 4

You will need to go back to the 1920s to see the word Aquastat printed on a control cover.

This was one that you might strap on to a pipe that is coming out of an old converted coal boiler. That's because Coal Boilers of the 1920s didn't expect to have oil burners or gas burners that needed high limits connected to them so there was no place to "Insert" the temperature probe. So the temperature was measured by the surface temperature of the hottest pipe near the boiler.

ethicalpaul · February 4

you are not paying for FUEL if the burner is not running, but the pump is still sending hot water to your radiators so all the heat is free!

Or at least "pre-paid heat" 😂

109A_5 · February 5

None of my cars or automobiles said car or automobile on them, my van does not say van on it, my motorcycles never said motorcycle on it, but that is their common name. Why do we drive on parkways and park in driveways ? I guess that is just the way it is.

So @EdTheHeaterMan how many folks did you convince about the free heat ?

ethicalpaul · February 5

https://forum.heatinghelp.com/discussion/comment/1886302#Comment_1886302

Leave it to the French!

109A_5 · February 5

https://forum.heatinghelp.com/discussion/comment/1886304#Comment_1886304

And a Dodge Caravan is confused (Car-a-van), however I never owned one.

EdTheHeaterMan · February 5

@109A _5, When you are talking to a person that is not technically savvy, and they insist that when the burner not running when the thermometer says it is 68° but the thermostat is set at 70° and they insist that something MUST be wrong with their thermostat, getting free heat sounds great to them. I have satisfied many a customer with FREE HEAT when I tell them the pump is still sending heat to the house.

You need to know your audience.

I hope that @MoreCowbell does not mind the fact that we took over his Discussion with this nonsense, or at least has a sense of humor.

Le Car. it really says that on "the Car". Ha Ha.

Bernie_the_Brewer · February 5

This puts me in mind of when I was learning about steam heat (in my previous house). I was confused about why the pressuretrol would turn off the burner, even though the thermostat wasn't satisfied. "Ooooh, I see. there is still steam, and it is still heating the house!"

MoreCowbell · February 5

Don't mind at all …

It's all good. Still wallowing in all the great information I gleaned on this thread !!

A very smart group … ☺️

EdTheHeaterMan · February 5

https://forum.heatinghelp.com/discussion/comment/1886328#Comment_1886328

You know that was FREE Steam… Right?

Bernie_the_Brewer · February 6

https://forum.heatinghelp.com/discussion/comment/1886380#Comment_1886380

Exactly! I thought that went without saying! :)

FWIW, I did recently set up an aquastat on my "new" hot-water system to run the circulator after the T-stat was satisfied as kind of a crude thermal purge. Rather have those "free" BTUs in my living room than my flue.

Valve remains open when boiler/circulation pump cuts off

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