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Danfoss ESBE VTC511 3-way Thermatic valve failing - should we keep it?

Because we have our snowmelt hooked into our main boiler the installer put in a Danfoss VTC511 to avoid temp. shock to the boiler.

Originally he put in a 140F temp. element but that caused too long of a lag time for the main boiler loop to heat up as it was only fully open at 140F+18F = 158F. He swapped the temp. element for the 131F so the boiler loop was fully open at 131F+18F = 149F.

Performance seemed OK but when all of our indoor floors were calling for heat we found the house was loosing temp. unless we ran the boiler at a High Limit of 190F.

Fast forward to today (when the low temp is expected to be -17F) and we have found that over the last few days of sub zero temp. the house heat was falling lower and lower. We looked at what was happening and the VTC511 is no longer closing the boiler bypass so the floor system only gets the smaller amount of heated water going around the main boiler loop.

To heat the house I have had to increase the boiler temp to 200F to allow a high enough temp to get to the 3 floor zones when the entire house is calling for heat. This makes me nervous about hitting the in-floor radiant tubing with two high of a temp when only 1 or 2 zones are calling.

If we have the VTC511 removed then I likely can run the boiler at 180F and not have a dangerously high temp (to the tubing) floating around in the system that could harm the tubing with only one zone going.

The first step will be to change the thermostat element to the 122F. If that doesn't fix it, replacing the valve is going to be a major pain. The installers had a devil of a time getting it in and I'm thinking of saying lets just take it out and remove the bypass, letting the boiler do what it was designed to and deal with any low return temp. that show up.

If you were me would you remove the Danfoss ESBE VTC511 3-way thermatic valve?


  • hot_rod
    hot_rod Member Posts: 19,881
    you have enough boiler to cover all those loads concurrently? Sounds like the valve is doing it's job of just allowing enough heat to large loads. Does that valve have temperature gauges at all 3 connections, or use a point and shoot temperature gun to see what is actually going on.

    What is the Cv of that valve? How many gpm are you trying to flow?.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Hot Rod,

    Thanks for replying.

    The boiler is 225 BTU so is sized for the loads. It is a Lennox GWB8-225IE-2. My recollection is that when it was working we could run the snow melt and still keep the boiler loops temps up. However I don't have notes to that affect so I could be wrong. Right now we are only trying to run our three house floor zones. So the load is very light.

    The valve was doing it's job as it was putting boiler temps around the main boiler loop. But not now. We have temp. gauges that show out of the boiler is 200F. But going to the floors is 165F with a 150F return (secondary loop). So to me this means very little 200F is going around the main boiler loop and the floor loop is reversing it's own return to mix the boiler temp. down. The return to the boiler (after the ESBE VTC valve is 200F. I can watch this pattern of the boiler out and boiler return equaling all up and down the temp. spectrum. It basically tanks to 13O-150F on the return on the main boiler loop (just before the thermatic valve) when I have the boiler temp. at 195F or 190F. However after the valve I am returning the same temp as the boiler output.

    So my interpretation is that the valve is somehow stuck with the boiler return wide open and is letting through very little main boiler loop water.

    I believe ours is the 1 1/4 inch valve based on eyeballing the near boiler piping. The Cv listed on the spec. sheet is 16.2. What does Cv stand for?

    The circulator is a Grundfos UPS26-99FC running in high mode. Not sure of what the GPM are but looking at the on-line spec. sheet it may be in the neighborhood of 28 GPM based on the loop height or about 4 ft. Not sure how much drag the boiler put on it going through the boiler.

  • STEVEusaPA
    STEVEusaPA Member Posts: 6,245
    Any chance you can show us pictures of the boiler piping or a sketch?
  • hot_rod
    hot_rod Member Posts: 19,881
    Piped like this?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • 4th attempt to post a reply. My appologies if all the old attempts show up.

    Here is a pic of our system.

    We have a ball valve on the bypass line so we thought of trying to throttle it but didn't want to damage the valve further. I called Danfoss to ask about this on Fri. but didn't hear back yet.

    We are piped just like the Return Mounted diagram on page 3 (second diagram). With the exception of the ball valve on the bypass.
  • Tim Potter
    Tim Potter Member Posts: 272
    I have the esbe, I believe its piped as you have it, & the beauty of it is, its bulletproof. Kind of like the t-stat in your car, only 1 moving part. if the element has gone bad, its a easy replacement.

    Any chance you have some kind of ghost flow on the snow melt siphoning off btu's? It doesn't take much -15* snowmelt water to pull down the 180* water to your house.

    The infloor tubing, if its designed correctly, doesn't need anything above 130* as I recall

    How are you limiting the tubing temperature presently?

    Winter Park, CO & Lenexa, KS
  • Hi Tim,

    It is good to know your VTC works well and reliably. Our installer sweated ours in and had a leak problem at one of the threads so it was sweated in and out at least three times which means it was hit with heat 5 times. I'm wondering if that damaged the internal plastic components of the valve. We are going to ask about union sweat connectors if the valve body needs replaced. If it can work well it seems we should keep it. What thermatic component do you have, the 122F, 131F or 140F?

    On our design documents, from 1994, the design temp is going to the floors is 130F. The loop lengths, zoning, heat load etc were all designed around this and if we can reliably get 130F to the floors they all heat up just fine. However the floor mass is too much if were sending 110-120F on cold days and the system can't reach temp.

    There is a small ghost flow on the snow melt but it doesn't really affect the system as there is a check valve on the snow melt secondary loop which keeps it to a minimum.

    Currently we use a mixing valve to limit the tube temperature. Our set up involves the boiler water going around a main loop. Then a secondary loop, with it's own circulator, pulls the hot water and sends it to a heat exchanger. We have a heat exchanger isolating the floors because they have old in-floor radiant heat oxygen permeable tubing. Then on the floor side a circulator pulls the hot water through the mixing valve and sends it to the floors. We have three floor zones that all have zone valves that open and closed based on calls from the thermostats.

    Our first step is to try and replace the thermostat element. However that component does seem to be working somewhat as it really tanks the system if the return temp is less than 131F. The problem seems to be that the boiler bypass portion of the valve never properly closes when the return temp is over 149F so we are getting most of the hot boiler water coming right back to the boiler and not going to the system.
  • Tim Potter
    Tim Potter Member Posts: 272
    edited February 2021
    I use the 131* for my cast iron boiler. It nails the boiler out at 138*, which is above condensing temp.

    I have injection mixing and use remote temp control, I can turn the house up from 55* away to 65* home from Kansas while I'm driving to Colorado. When I change the temp, even though I'm dumping hotter water in the the loop, the Floor mass (in floor gyp) absorbs it like a sponge, my deltaT goes to about 20* until the floor mass heats up then the delta smooth out to about 5* steady state.

    As I recall, the Body of the esbe is cast iron, so if you replace the thermostat element, It should work as planned.

    Can you isolate the snowmelt completely ???? might be worth it to see if its enough "drag" on the system to cause problems.

    You said: "Currently we use a mixing valve to limit the tube temperature." what's the Cv on the mixing valve? and what's your infloor deltaT on all your loops??

    Winter Park, CO & Lenexa, KS
  • DJDrew
    DJDrew Member Posts: 81
    edited February 2021
    I had the 131 element in my system early on and found it throttled everything too much. In talking with the manufacture of our boiler, they recommended I use the 122 element. The 122 element was an easy swap and seems opens up earlier to allow full system flow quicker. Even with the 122, my system will plug along nicely at 133 for an hour.

    ESBE VTC Temperature Element (122 F)

  • hot_rod
    hot_rod Member Posts: 19,881
    I have the Caleffi brand and found the same issue, I bought the 140F, and ended up dropping to the 115F.
    The balance valve is fairly important to make that valve work, as I understand it. I'm not sure about the valve on the second bypass, but the one on the valve piping needs adjustment sometimes.

    If that one has plastic components inside it may have been damaged, or the copper heat motor could have been fried. It always wise to remove "innards" when you sweat large brass valves that take a lot of heat.

    Looks like you have isolation on at least two side for service?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Tim,
    Your system is more modern than ours. Our original install was in 1994 and then we replaced the boiler in 2016. Since the replacement we have had many problems with the new system. With respect to this valve the original 140F thermostat element took too long to come up to temp so we replaced it with the 131F. But even with that element we had to elevate the boiler temp. from it's original high limit of 180F to 190F to get enough heat to the floors.

    We blamed it on the triangle tube heat exchanger. When our newish (2016) expansion tank for the floors rusted out a few months ago we reverse flushed the heat exchanger and got alot of crud out. We also found deposits of rust/particulate matter that occassionally came out when we were flushing the floor lines. I do not recall the installers flushing the lines so some may have been blocked up with crud that was getting caught in the heat exchanger. We had oxygen permeable tubing and cast iron circulator along with a cast iron boiler so there was alot of crud in the tubing.

    The current problem is with the ESBE VTC not ever closing the boiler bypass. We had a nice long chat with a very helpful Danfoss rep. today. The problem could be a bad thermostat element. We have the 122F on order. But the problem also could be something caught in the boiler bypass valve keeping it from ever closing. Or (because the installers had to sweat it in and out 5 times) the internal plastic component of the boiler bypass valve may have been damaged/weakended and subsquently broke.

    In terms of your other question:
    We have the AM-1 STD model mixing valve on our 3 floors and the AM-1 R model on the basement. Why the difference? Who knows. I forgot to look what was the mixing valves for the garage heat and snow melt.
    The AM-1 STD has the following characteristics.
    Mix temp of 100°F - 145°F (38°C – 63°C) STD Domestic hot water and heating applications.
    Hopefully it really doesn't put out more than 145F which would alleviate my fears of us sending too high of a temp to the floors when the boiler puts over 180F across the heat exchanger. The spec. sheet says we can limit the high end but since it is marked as factory limited at 145F we aren't going to mess with it.

    I had the Danfoss guy tell me what the Cv was but I couldn't really follow what to do with it other than ask him if our boiler main loop circulator was appropriate. He thought it might be oversized however he didn't seem to think it would be overcoming the ESBE VTC valve. He did think we could partially close the ball valve on the bypass loop to limit the amount of water bypassing and see what happened. We may try that when we get brave. I hate messing with it when we have such low temps as if the VCT valve internals break more maybe they would prevent the boiler loop from operating at all and then no heat.

    We could isolate the snow melt completely but there isn't enough parasitic drain to do what we are seeing. The floor secondary is prior to the snow melt secondary. Also the place were measuring the return temp is after the snow melt secondary. And we see that with 200F we can get 150F back so the boiler bypass should be fully shut and the main loop fully open. From the measured temps we can see that isn't happening.

  • DJDrew,

    Thanks! We are switching to the 122F element and hoping for the best. I checked our boiler manual and 120F return is the low end spec. so we probably should have gotten that element to start with.
  • Hot rod,
    Nice to hear that even an expert sometimes ends up with the wrong thing.

    No really good service isolation as the main boiler loop will have to be drained. In terms of sweating the Danfoss rep recommended union connections to protect the inards. No mention of that in the installation documents. May have been OK if they had got a good connection the first time but they didn't. The threaded bypass connection was leaking several times so it was sweated, hit with cold water-leak found, unsweated, resweated, hit with cold water-leak found, unsweated, resweated and hit with cold water. Maybe even one or more time beyond that. Likely any plastic would be stressed with that treatment. It was installed in Feb. so the fill water was icy cold.

    I know when the head boiler installer finally got a good connection he went out to his truck for something. The assistant got some water and splashed it on the valve and reported to the head guy that it was still leaking. He just about had heart failure before the assistant said "gotcha". There was much swearing and promises of payback.
  • hot_rod
    hot_rod Member Posts: 19,881
    Those Honeywell mix valves are lie Cv, probably 3.  So tough to get more than 6 or so gpm without a high head circ. Any offers how much flow or BTU those zones require?  Could be bottled up in the mixers

    They too needs cleaning from time to time.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Hot rod,
    The flow rate on the design documents shows a total of 4.1 gpm for the three zones on the two floors. Thankfully it appears the mixing valve is OK.
  • Good news! We replaced the thermostat element with the 122F and all is working now. My husband did it himself and noticed when you put the thermostat element in that it leans down a bit. So he seated it in the cap and inserted the whole assembly.

    We tested the system and running the boiler at 180F delivers the heat to the heat exchanger and thus the floors just fine! We have had a problem with this system since it was installed (5 years ago!) and though the heat exchanger was undersized but it turns out it may have been the thermostat element was not installed properly so the boiler bypass was always open.

    I can't believe it. For the first time since this boiler was installed in 2016 all the temps did what they should have. The boiler seems to going back to normal cycling and not be short cycling.

    I would love to test the snow melt but the switch to turn it on that our boiler installation company installed caught fire in the wall so we got a replacement and hired an electrician to install it but it was bundled with a bigger project for a generator and due to the ground being frozen we have to wait until spring. I don't want to have the boiler installer do it because they didn't do it correctly last time.

    Thanks to everyone who said their valve worked just fine. Hopefully if anyone else has this problem with the valve they can check to make sure the thermostat element is properly seated.
    STEVEusaPATim Potter