Valve remains open when boiler/circulation pump cuts off

MoreCowbell

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

" 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

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

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

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

MoreCowbell

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

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

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

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

109A_5

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

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

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

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.