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  1. George Webster

    George Webster New Member

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    I am new to this forum. I have an Attack DP35 Profi, DHW FPHX and two hydronic floor zones, 100' each. My recirc loop uses a Danfoss ESBE VTC511 1" FNPT with a 140F thermostat. On startup, when there is a call for heat, my return temperature quickly drops to 120. As the zone heats, it of course comes back up, but then I activate the next zone, same thing. My understanding is the Danfoss begins to open at 140, so if your supply is 180, there is no reason the return should be less than 140, unless the valve is not working. Another odd thing is that I have an analog temp/press gage located in the supply about 5" from the boiler outlet. It reads 10F lower than the indicator on the boiler, even though it's only 5" from the boiler's sensor. I have verified this with an infrared thermometer and that's really what the temp's are. The boiler goes into idle with the supply at 180F+ and the return at 120F. Once the zones heat to normal operating temps, the return is of course fine and it seems to operate reasonably well. Because of condensation concerns, I don't want to continue running it until I figure out what's going on. Any thoughts out there?

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  2. BoilerMan

    BoilerMan Minister of Fire

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    Welcome to the Hearth! What kind of temp gauge do you have. My strap-on temp gauge reads 10-12 degrees higher than the boiler. The boiler temp reading can be confirmed by an IR non-contact thermometer. Can you remove the thermostat from the Danfoss, and put it in a pot on the stove with a thermometer to confirn it is opening at 140? I do this with all thermostats I install, including automotive ones.

    TS
  3. George Webster

    George Webster New Member

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    It's a dial gage. The problem I see is that the valve is supposed to just begin opening at 140, so the return temperature should never drop below that. If the valve were sticking, I would get low flow and the return temp would be higher than 140. I'm trying to figure out if it's teh valve or some other restriction causing low flow. I'm hoping to find someone with direct experience with this valve.
  4. Nofossil

    Nofossil Moderator Emeritus

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    I've looked at this - it's strange. I don't have experience with the ESBE valve, but it's definitely installed properly, and it definitely is allowing VERY low return temps. Is there any history of these things sticking / failing? If the boiler is at temp, what's the lowest return temp you'd expect coming out of the valve?
  5. The esbe valves have different thermostat elements available. Are you sure it is not a 120 degree element? I'd imagine if you pulled the element it would be stamped with a rating or part number.

    The lowest return I'd exepect to see once the boiler is running is what the element is rated for.
  6. Fred61

    Fred61 Minister of Fire

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    Where are you checking the return temperature? Boiler side of the Danfoss or return side before Danfoss? The hot boiler supply temperature flows to the bulb on the automotive thermostat through the bypass and activates it which will allow a small amount of system return flow through the Danfoss so if you are checking temperature before return water enters the Danfoss, you will measure the actual return temperature of the water. It's not like the thermostat senses 140* and pops open. It's going to start opening when water from bypass reaches 140* and as soon as the return water temperature is sensed, it could close or only stay open enough to mix some return water with bypass flow to maintain 140*.
    So temperature on the return side could be room temperature water that was in the loop but there would not be much flow until the return water starts approaching 140*.
  7. Nofossil

    Nofossil Moderator Emeritus

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    Hi Fred - nice to hear from you again. Another EKO 25 user, too! We should talk about puffing and fine tuning some day.

    Back on topic, the temp is measured a couple feet downstream from the ESBE outlet - actually, between the boiler circ and the boiler. If memory serves, it's set up ESBE -> circ -> boiler inlet. Listening to what you and Mike are saying, I'm thinking that this valve is not working right. If the boiler outlet is 180, then there's no way the inlet should be 120 for more than a few seconds, and that only when a zone opens and sends a slug of cold water that makes it through before the valve can respond.

    I'm assuming that these things always allow flow, and should only be selecting how much of that flow comes from each inlet.

    It looks like this one either (a) allows WAY too much cold water through, or (b) shuts down flow almost completely so that little or no hot water can recirculate.

    Also sounds like verifying the cartridge (hot water pan test on stovetop, I think) might be a good move. Sound about right?
  8. Fred61

    Fred61 Minister of Fire

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    I totally agree that if return temperature is measured after the outlet of the Danfoss the temperature should be 140 or above. When reading the post, I didn't get the message that the temperature was being measured downstream from the Danfoss, that's why I asked. My detailed (and confusing) explanation was to demonstrate why he could see lower temperatures if he was measuring on the upstream side. If the thermostat only opens a crack, it could take quite a while to allow water from 100 feet of pipe to seep through the valve when it is trying to maintain 140* water with 180* coming from bypass mixing with room temperature water coming from the loop.
    As an afterthought. I wonder if playing with the throttling valve in the bypass line, perhaps allowing more flow (or less) would change the way it is behaving.
  9. BoilerMan

    BoilerMan Minister of Fire

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    Sorry for saying this again, but take the thermostat out, and put it in a pot of water on the stove. Measure the water temp and see when it starts to open...........should be 140F if thats the element that is in there. I've done this many times and found thermostats from the factory bad on rare occastion.

    TS
  10. George Webster

    George Webster New Member

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    Good thought, I'll check that when I get a chance. Although I do recall checking that when I first got the unit, just to make sure it had the correct one before installing it. If memory serves, it has the Danfoss part number stamped on it, and it did correlate to the 140. I'm going to do another test brun tonight to get as much information as i can, based on questions and responses to this post.
  11. George Webster

    George Webster New Member

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    I did not include a throttling valve in the bypass, as there was no reason to. The whole idea of using the Danfoss. I do have circulator isolation valves, but that won't help as far as I can figure. One thing i didn't mention is that this is a combination system - backup oil boiler. I have run that the past couple of days to both avoid condensation in my wood boiler and to test a few things that could cause this problem from a system perspective. When the oil boiler is fired (System 2000), it has a 2-3 minute warm up before activating any zones. I timed the zone for temperature rise at the return after initial zone valve opening and calculated about 2GPM. Unless the circulator on the wood side has issues, it should be giving identical performance, provided the Danfoss is allowing flow. I will try the same timing measurement with wood tonight.
  12. George Webster

    George Webster New Member

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    Sorry if I gave you the wrong impression. I will do that tonight. One thing that bothers me here and seems to make no sense - perhaps you could shed some light. If the Danfoss is working properly and the element is opening too soon, enabling much colder water to enter the boiler, then why does the boiler go into idle mode? It's like there isn't enough demand, yet the return water is at 120. This only happens at startup and all I can think is that because I'm waiting for the return temp to increase before enabling additional zones, there isn't enough flow to cool the bolier sufficiently, but the water that IS entering the boiler truly is that cold. make sense? The initial zone I activate is my DHW FPHX, which is fairly small, but does impose a pretty hefty load initally due to high delta T. Still, it's just a 1/2" MNPT fitting, so only so many BTU's can exchange.
  13. BoilerMan

    BoilerMan Minister of Fire

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    Ok, I think I'm following you now. You either have a control issue, but more likely your not moving enough water, this has been said. High delta (you have) but not enough flow = not enough btus moved out of the boiler, too high output temp = idle. I'm sure I've missed something, following the election on the news right now..........

    TS
  14. George Webster

    George Webster New Member

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    OK, I have it working, but not sure why. I fired it up last night and it simply worked. All I can think is that I had an air bubble in the circulator, causing cavitation and significantly reduced flow. I added the wood boiler late last season and did some significant replumbing in prepration for this year. In setting up my control system, I mkanually activated the circulator a couple of times, with no zones active. All I can guess is that broke the bubble loose. Thanks to everyone who responded to this thread. It really stimulates the thought process. Now back to the storage issue ....
  15. Fred61

    Fred61 Minister of Fire

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    I'm still concerned or maybe confused about your statement above that you didn't install a throttling valve in your bypass. Since water will take the course of least resistance, wouldn't most of the flow just keep circulating within the boiler loop thus reducing the flow from the heating loop? Or am I missing something?
  16. George Webster

    George Webster New Member

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    The Danfoss valve I have installed takes care of all that. It's actually a very clever device. Basically, it has an automotive style thermostat that begins opening at 140F. Before it opens, it is doing just what you say, directing much of the boiler output right back to the return, preventing low return temp. At that point, very littel flow is being directed to the demand zones. When it begins opening, it simultaneously begins closing the recirculation loop. It's designed to maintain constant flow through the boiler, based on the combination of recirsculation from the boiler output and return from the demand zones. Once the return from the zones reaches a temperature above 140F, there is little or no recirculation flow from the supply side - most if not all of it is now directed to the zones, satisfying heat demand. The important thing is that it is now working the way it's supposed to. I've attached the cut sheet. I'm once again heating with wood! Now to get that storage working .....

    Attached Files:

  17. George Webster

    George Webster New Member

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    Just a side comment on your signature block. Couldn't agree more. I have a 455 rancher, 20" bar. Most awesome, relaible, fast cutting saw I have ever owned and lightweight for it's capability. Cost twice what the piece of #$@! Homelite 20" cost, but it didn't even last 2 hours. Back to Home Depot, off to Lowe's for a real saw. I've had it for 3 years and couldn't be happier.
  18. maple1

    maple1 Minister of Fire

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    Ah yes, the old throttling-valve-in-the-danfoss-bypass-loop debate.

    I never could get my head around that one, and why a valve would be necessary - I just eventually came to the conclusion that it was necessary to compensate for some kind of design shortcoming in the Danfoss. Perhaps the ESBE is a re-design or update to fix that? There is definitely no valve called for in the diagrams in the attached PDF above - a good thing IMO.
  19. George Webster

    George Webster New Member

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    Don't know about the old valve, but if you look at the spec on the ESBE I believe the leakage is very low, on the order of 3% of total flow, once the valve is fully open.
  20. danjayh

    danjayh New Member

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    Do you have an aquastat on your boiler? If so, does just the return temp get low, or does the water in the boiler actually get too cold too?
  21. Bob Rohr

    Bob Rohr Minister of Fire

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    I think the throttle valve has to do with the temperature of the element PLUS the differential. The return port is fully open when the temperature is 140° PLUS the 18° differential= 158° is reached. So the valve needs 158° before the return port is fully open, bypass off, not the 140° or whatever the element temperature is. In other words the bypass is still allowing flow until the return is 158°.

    I think this is why installers try to add a valve to throttle thinking the valve is not sensing or working properly. Anytime you put a valve and throttle it you are reducing the gpm flow thru the valve, that presents as the boiler reaching high limit and shutting down, yet there is still a load that is not being satisfied.
  22. jebatty

    jebatty Minister of Fire

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    IMO Bob is correct on this. I have a balancing (throttling) valve on the Termovar on my Tarm. My design is for the Tarm to heat storage only, and then storage supply the system. With cold storage water, generally below 120F, the balancing valve is essentially wide open. This would be typical of shoulder season or cool weather operation when I run my storage down to about 90F before re-firing the Tarm, and then only fire the Tarm to bring storage up to about 160F. This may provide 3-7 days of heat before the next firing.

    With cold winter operation, +15F to -30F or lower, I close down the balancing valve considerably, and now I usually don't let storage drop below 120F-140F, and heat storage to as much as 190F top to bottom on Tarm firing. This provides 2-3 days of heat before the next firing.

    This use of the balancing valve is totally consistent with Bob's explanation of the effect of the valve on the boiler.

    As my other posts have indicated, since I always do weighed wood burns, the Tarm always operates on maximum burn to fire out and never any idling.

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