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Old 09-23-2011, 09:02 AM   #1
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some registers hot w/ thermostat off


I've got a pretty simple 2-zone hydronic system with baseboard registers. This summer, I noticed the first 2 (short) registers on the upstairs zone were hot, even though both of our thermostats were set to "Off". I decided to just close off the upstairs zone using the shutoff valve, and I figured I'd deal with it in the Fall.

Well, now it's the Fall...

I suspect it might be caused by a leaky (partially-open) zone valve. Before I go thru the trouble of draining the system and pulling the head off the zone valve, any advice or suggestions from the experts here would be most appreciated.


JohnB

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Old 09-23-2011, 03:58 PM   #2
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some registers hot w/ thermostat off


You very well may be correct. However, the only reason why the boiler should be running in the summer would be if you have a Domestic hot water loop. Do you? If yes, then ok. If no, then the zone valve module may be calling for heat because it is sticking. First thing to do is open the shutoff that you closed and then turn on the other zone to call for heat. next, remove the possible faulty module and check to see that the zone closes by verifying the line temp on both sides of the zone valve. If the pipe is not hot on the outlet side then the valve works and then you just need to check the module.

What zone valve model is it?

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Old 09-23-2011, 04:36 PM   #3
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some registers hot w/ thermostat off


Yes, my boiler is also my tankless h/w heater, so it runs year-round.

I assume if the zone valve is not completely closed (but the circulator isn't running), that might allow for just enough convection to heat just the first 2 registers upstairs. Does this sound plausible?

My water is horrible, so I wouldn't be surprised if some accumulated scale is causing the zone valve ball to hang open a little bit.

btw, my zone valves are the common Honeywell model V8043E. I've replaced the heads before, but never the actual valve body.

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Old 09-24-2011, 07:15 AM   #4
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some registers hot w/ thermostat off


Are your zone valves on the return or supply.
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Old 09-24-2011, 09:55 AM   #5
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some registers hot w/ thermostat off


They're on the return side, right before the circulator.

Since I've never had this problem before (I've lived here for 8 years), and since it only affects the upstairs zone, I'm thinking it's almost got to be a leaky upstairs zone valve.

I'm gonna drain the system and check out the valve tomorrow. I'll post the results here.

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Old 09-24-2011, 10:53 AM   #6
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some registers hot w/ thermostat off


Could easily be your aquastat is not working right, and heating up the water too hot.
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Old 09-24-2011, 02:18 PM   #7
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some registers hot w/ thermostat off


Thanks for the suggestion. I've got the HI Limit on the aquastat set to 180, and after a burn cycle the temp gauge on the boiler reads about 200-205. I think this is pretty much the way it's been for the last 8 years. I've always just chalked it up to the temp gauge being a little off, and I've been told by a few HVAC guys that it's ok. Maybe you can tell me differently.

Also, I've got an Intellidyne Heat Manager installed, and the temp probe on the heat outlet pipe reads about 189 after a burn cycle.

Besides, if my boiler temp was too high, wouldn't the first register on the main floor zone be hot as well?

Any advice is much appreciated.
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Old 09-24-2011, 04:16 PM   #8
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some registers hot w/ thermostat off


The water takes the path of least resistance, and the first floor zone may not be that path.

Why is the heat manager leaving the water temp gt so high. Its not 0 degrees outside where you live at already is it. If the high limit is set to 180, what is the low limit set at, and are you using heat already?

The high limit should shut the burner off at what it is set for. A small amount of temp rise is ok. But, it shouldn't be cycling on the high limit, that is not its purpose.
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Old 09-25-2011, 11:05 PM   #9
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some registers hot w/ thermostat off


Thanks so much for the input.

Quote:
Originally Posted by beenthere View Post
The water takes the path of least resistance, and the first floor zone may not be that path.
Yes, you're right. You would think the ground floor zone would be the path of least resistance because of the height/lift factor, but I guess that's not necessarily the case.

Quote:
Originally Posted by beenthere View Post
Why is the heat manager leaving the water temp gt so high. Its not 0 degrees outside where you live at already is it.
With the Intellidyne Heat Manager, the high cutoff is still determined by the Hi Limit control on the aquastat, just like a "normal" system. Also, just to clarify, the Intellidyne doesn't utilize an outdoor temp probe like some other heat managers.

Quote:
Originally Posted by beenthere View Post
If the high limit is set to 180, what is the low limit set at, and are you using heat already?

The high limit should shut the burner off at what it is set for. A small amount of temp rise is ok. But, it shouldn't be cycling on the high limit, that is not its purpose.
I've always kept the aquastat high limit at 180, and the low limit at 160. As I said in my earlier post, I've always just assumed that the temp gauge was off and reading 20 degrees high. But now I realize it's more likely that the aquastat's bulb is 20 degrees low, and therefore the water is being heated too much - just like you suspected.

As an experiment I turned down both aquastat controls by 20 degrees (160/140), and now the burner cuts off when the temp gauge reads 180 - just like it should. I then re-checked the 2 upstairs registers, and they're still warm to the touch - but not downright hot like they were previously. So I think this is probably the main cuplrit. I still think I might also have a leaky zone valve.

Anyway, it seems like I'm gonna have to replace the aquastat. But before I do that, it probably makes sense to drain the boiler & check the inside surface of the temp bulb well for scale buildup, which could possibly be acting as a heat insulator between the water & the bulb. Know what I mean?

Once I get the temp issue under control, then I'll take a look at the zone valve. Of course, I'll post my results here.

best,
JohnB

Last edited by johnnyzero; 09-26-2011 at 11:29 AM.
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Old 11-08-2011, 09:06 AM   #10
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some registers hot w/ thermostat off


I just wanted to post an update. The problem with the always-hot registers turned out to be a leaky zone valve, as several posters suggested.

Unfortunately, the high temp problem still persists, even after replacing the aquastat. I created a new post about this this issue with the topic name "boiler temp overshoot".

JohnB

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