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Need recommendation for manual reset high limit setting on Ultra boiler

JoeJoe Member Posts: 16
A friend just had a new Weil McLain Ultra boiler installed that serves both radiant slab on grade and suspended tube below wood (no transfer plates) floor type zones. He also had an indirect installed for his domestic hot water.  His contractor missed the need per the installation manual for a field installed high limit control installed on the radiant manifold which would protect the radiant zones from overheating, especially the wooden floors.  Question, what setting would you set it? The manual didn't suggest one.  FYI, the installer has decided to use the slab on grade setting on the Ultra so the maximum supply water going to the zones will be 120 F.  Also, the installation manual allows either an automatic resetting or a manual resetting control, which is better?  I think either control would need "resetting" at the Ultra's control panel so maybe there isn't a better choice but for sure there needs to be one.  I could use some field experience with this one, thanks in advance.  Joe


  • bill nyebill nye Member Posts: 307
    Manual reset

    Manual reset may not be a good idea. If you are away from home and no one is there to reset it, the house could freeze ?

    I simply used a 6006 aquastat set to 140° F. It breaks on temperature rise and will stop the circulator pump to my floor heat zone. I have staple up , no plates, and I am designed for about 130-135° on a 0° day. It has never got there. If it did reach hi-limit and stop, the pump would automatically resume when the water cooled a few degrees.
  • ZmanZman Member Posts: 3,516

    Is the DHW piped separately (parallel) and prioritized?

    If so why would you need a high limit for the radiant? The boiler is controlling the temp and has a high limit to protect itself. Why would the radiant get hotter than the set point?

    I would be concerned that the slug of hotter water that can hit radiant side when the boiler switches out of DHW priority would trip the high limit on the radiant side. It would not be enough to damage the floor. I think the requirement is a CYA for mis-installed systems.

    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • JoeJoe Member Posts: 16
    Just going by install manual

    Bill, great point on the auto resetting of the limit when nobody is home.  Also, Weil McLain specifically calls for a field installed high limit whenever you program the board (U-Control) for low temperature applications if you also have a high temp application too, ie DHW.  The Weil McLain manual uses capitol bold letters on the DO NOT when they say don't rely on the boiler control to protect your low temp systems from overheating.  By the way, the boiler is a 105 Series 3.  I'm thinking to suggest a 150 F setting to begin with and see what happens. 
  • heatman101heatman101 Member Posts: 19
    My thoughts...

    This is a case where the manufacturer is covering their butt for liability you choose to install the limit, then set it 5 degrees above the max. DHW boiler setting. Then hook it to the soft lockout or auto resetting terminals on the boiler. Then if it does open, the boiler should restart when it closes again...the Honeywell 6006 strap on should work well.

    On another note....I would never even consider installing radiant tubing under a hardwood floor without using transfer plates.....that's asking for trouble....
  • ChrisChris Member Posts: 3,056
    Missed The Need?

    Don't see where that is an installation error. You stated the contractor missed the need. Nothing is missed. I'm going to assume your friend has the heat loss and radiant design right? Your dealing with a low temp and high temp radiant so they both have mixing valves correct? The boiler has the ability to cap off the highest supply temp correct? The boiler has an adjustable high limit correct? So where's the need?

    I'm only stating these because your up here putting the blame on the contractor, ever think there was a reason why? The piping schematics in the manual are CONCEPTUAL!
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • JoeJoe Member Posts: 16

    If a manufacturer of a boiler has specific piping requirements and the installer choses not to follow them, there better be good industry accepted practices that he can refer to inorder to show why he differed from the manual.  On this specific job the contractor missed multiple piping requirements and when confronted his statement was along the lines of "I've been to the classes and don't need to look at the manual."   Things that were missed: pumping away, no air elimination device, zone pump (4 zone valves, P/S pumping-relying on boiler pump to somehow pump the water thru the zones) 2 different types of radiant (slab on grade and suspended under wood) without mixing valves.  I was asked to take a look at this job and in as friendly of a way as possible suggested to the installer how and why his work needed to be modified.  I consistently referred him back to the manual along with industry accepted practices such as pumping away.  I feel I have been true to my friend (he just wants a system that will work properly and run as efficient as possible) and have tried to share with this contractor that reading the manual and books such as Pumping Away will only make his life easier...  
  • ChrisChris Member Posts: 3,056
    Your Post Was Concerning

    A high limit not all the other items of concern you just posted. A piping diagram in a manual is conceptual. If I installed a low loss header instead of 2 closely spaced tee's and didn't use a Spirovent or Air Scoop would I be wrong? Nope, If my expansion tank and feed are piped on the primary side below the boiler pump am I wrong? Nope.

    If I put my secondary pump on the return and my zone valves on the supply am I wrong? Nope. In other words the manual is not a bible to installation, its merely a map that can be adjusted, providing you still maintain proper piping practice.

    If I decided I didn't want to use that boiler/primary pump that came with the boiler am I wrong? Nope. My point is a piping diagram is conceptual and can deviated from providing you still maintain proper piping principals. I don't need a high limit for my radiant under all conditions and honestly one is rarely if every used. Why? Proper piping, control and installation.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • heatman101heatman101 Member Posts: 19


    It is good that you are looking out for your friend....

    It is obvious that this contractor has either no experience with this boiler and is not interested in installing a system correctly, but installing for the least cost.

    This system will NOT work as installed...while I agree that the high limit is not needed for the system to work, things like using only one pump will cause the system to not work. Yes, parts and pieces can be substituted here and there, but there are portions that simply cannot be changed. The trick is to know the difference, and this contractor does not have that knowledge.

    I would fire the installing contractor and find one with experience installing the Ultra boiler. Yes, that will cost more $$, but your friend deserves a system that will work properly.

    Kudos to you for getting on here and trying to find the truth for your friend!
  • JoeJoe Member Posts: 16
    edited October 2013
    You are right

    My original post really concerned a high limit setting however as I received replies I thought it may add to the story, some of the other items that happened on this job.  What do you think would happen if the wood flooring overheated, cracked, buckled and needed to be fully reinstalled?  I would think the home owner (my friend) would look to the flooring guy who then would look at the installer who would feel as if he did nothing wrong and then would look at the boiler manufacturer.  Now, if in the boiler paperwork there was a big bold warning about a field installed high limit, especially if you have these certain conditions, and it's not there...... 
  • JohnNYJohnNY Member Posts: 1,822
    You're referring to this paragraph, I guess:

    Multi-temperature systems — If the heating system

    includes circuits that require lower temperature water

    (radiant slab circuits, for example) as well as higher

    temperature circuits, it is recommended to protect lowtemperature

    circuits with limit controls that are wired to

    a U-Control external limit circuit (P13 terminals 1 and 2

    for manual reset, or P13 terminals 3 and 4 for automatic


    2. See instructions beginning on page 26 for wiring information.

    a. Manual reset operation: If external limit controls are to cause

    manual reset of the U-Control module, connect series-wired

    isolated contacts to P13 terminals 1 and 2 (see page 26 for wiring


    b. Automatic reset operation: If external limit controls are to

    cause automatic reset of the U-Control module, connect

    series-wired isolated contacts to P13 terminals 3 and 4 (see

    page 26 for wiring information).

    c. If using a manual reset limit control or wiring in the manual

    reset circuit, set U-Control boiler limit at least 20°F less than

    the external manual reset limit (i.e., set U-Control no higher

    than 180°F for a 200°F external limit, for example).

    Weil-McLain simply wants to make sure there is some device between their product and a buckled floor.

    There are any number of ways to do this including, as they explain in different words, an electronic aquastat to create either a hard or soft lockout, or perhaps even a manually operated tempering valve.

    Generally speaking, you don't want a hardwood floor to exceed a surface temperature of 85°F. Depending on a whole bunch of stuff, that may mean limiting the water temperature in that zone to ~95°. But, I'm over here and you're over there, so you're far better off letting a seasoned pro put his eyes on the project.
    For private consulting services, find John "JohnNY" Cataneo here at :
    "72°F, LLC"
    Or email John at [email protected]
    Or at Gateway Plumbing & Heating
    John travels regularly to out-of-state clients for consulting work.
  • ChrisChris Member Posts: 3,056
    Doubt the Boiler Mfg

    Boiler is a heating plant, period, end of sentence!!! It is a piece of equipment that produces heat and has no responsibility as to the system side. If the boiler is operating it isn't broken and the mfg end of the chain is done. Since when did the boiler mfg size, design and recommend the radiant heat? It did not. No different then the cheap HDMI cables that come with that nice 60 plus inch flat in the living room, it works right? Does that manual tell you they are the cheap cables and to go out and buy some monsters because the pic will be 10 times better?

    Its funny how our industry is scrutinized so deeply by the blind and internet educated DYI consumer. Bet your friends installer was the cheapest guy that bid the job.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • JoeJoe Member Posts: 16
    Awfully sensitive Chris, aren't we?

    I've learned in my 30 plus years of HVAC work that people assume plumbers know everything about hydronics.  The technically "blind" consumer just assumes that if it concerns water and pipes, it's a plumbers job.  I have come to appreciate that if we didn't properly supply fresh water to ourselves and correctly deal with our wastes, we all would be sick or dying so I am in no way blaming all plumbers but the plumber in question on my friend's job is at a point in his career where if he wants to play with the big boys then he has to do his homework.  Homework like this website, Dan's books, Dan's seminars and most importantly the willingness to accept new ideas.  
  • ChrisChris Member Posts: 3,056
    Not Sensitive

    Just tired of consumers in general, whom after choosing the cheapest installer come here to complain about their installation and/or contractor, ask for the solution or guidance, when they had the solution the entire time but did't want to pay for it.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • VA_BearVA_Bear Member Posts: 50
    I can see...

    the use for a limit thermostat on the low temp loop for a hardwood floor radiant loop for the day that the mixing valve fails and overheats the loop, if nothing else than to prevent a damaged floor and the resultant claims.
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