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  1. #1

    Weil Mclane ultra 155 settings

    I currently heat with an outdoor wood boiler. This maintains the water temp going through my WM-ultra at about 180°. The heating limit on the ultra is set to 150° as a backup if the fire goes out. At this setting, when the house calls for heat, the boiler does not fire. The readout says that the system is satisfied. When the hot water tank calls for heat, the boiler fires and maintains 190°. I have the setting on the DHW at 140°. Any idea why its firing to 190° when I have it set for 140°?

  2. #2
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    I think I know what you are asking...

    When the domestic hot water aquastat calls, most of the internal controls on the mod / con boilers automatically ramp the boiler output to 180 or 190 to maximize domestic hot water recovery. They also usually disable teh pump that runs through the boiler and feeds into teh heating loop, and enable a pump in-line with the indirect tank.

    You could do some piping and controls trickery to heat the domestic hot water with the wood boiler if you wanted, depending on your ambition and budget level... In other words, if the wood boiler loop is over say 160, divert the water through the indirect tank with a three-way valve when the dhw calls. I would pipe the indirect tank "first" in series with the house radiation, to maximize the delta t between the domestic hot water and the water you are heating it with...

    Sorry, I'm an engineer, I'm always thinking of better ways to do hydronic systems...

    Otherwise, it sounds like things are operating how I would expect, based on what I know...

  3. #3
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    Cool

    Quote Originally Posted by larobj63 View Post
    I think I know what you are asking...

    When the domestic hot water aquastat calls, most of the internal controls on the mod / con boilers automatically ramp the boiler output to 180 or 190 to maximize domestic hot water recovery. They also usually disable teh pump that runs through the boiler and feeds into teh heating loop, and enable a pump in-line with the indirect tank.

    You could do some piping and controls trickery to heat the domestic hot water with the wood boiler if you wanted, depending on your ambition and budget level... In other words, if the wood boiler loop is over say 160, divert the water through the indirect tank with a three-way valve when the dhw calls. I would pipe the indirect tank "first" in series with the house radiation, to maximize the delta t between the domestic hot water and the water you are heating it with...

    Sorry, I'm an engineer, I'm always thinking of better ways to do hydronic systems...

    Otherwise, it sounds like things are operating how I would expect, based on what I know...
    I agree. We have a lot of these setups around here and that is pretty much what we do to solve this problem.
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  4. #4
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    Thats the setting from factory.

    You can ask your contractor to reset it, if you want. if you don't have a high hot water demand, no problem resetting it to 170, maybe even 160.

    I've set several lower then what the factory recomends. No problem, unless they have a high demand(more then 100 gallons in 30 minutes on a 40 gallon tank).
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  5. #5
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    Quote Originally Posted by beenthere View Post
    Thats the setting from factory.

    You can ask your contractor to reset it, if you want. if you don't have a high hot water demand, no problem resetting it to 170, maybe even 160.

    I've set several lower then what the factory recomends. No problem, unless they have a high demand(more then 100 gallons in 30 minutes on a 40 gallon tank).
    Well, right, but..

    Depending on how it's piped, the DHW tank is likely a parallel circuit piped into the gas boiler injection loop, with checks in both circulators. If this is the case, piping changes need to be made in order to actually heat the dhw tank with the wood boiler loop. If he does what you describe, at least the gas boiler will be running more efficiently, in theory.

    Would need either lots of photos, a schematic, or a site visit to know for sure. I'm just guessing at how this is piped, based on what has been described, and the near boiler piping schematics that usually come with the mod/cons.

  6. #6
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    Since he said the wood boiler maintains the temp in the boiler.
    I'm guessing its already piped up that no other modifications are needed.
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  7. #7
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    Quote Originally Posted by beenthere View Post
    Since he said the wood boiler maintains the temp in the boiler.
    I'm guessing its already piped up that no other modifications are needed.
    Depends. The gas boiler system supply sensor could be in the wood boiler heating loop.

    I was thinking the gas boiler is injected into the wood boiler heating loop, so you don't fight the head of the gas boiler all the time.

    At least, that is how I would do it, but you would need additional complexity to heat the dhw with either source...

    It could be either way, like I said, would need to see it.

  8. #8
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    The sensors of the Ultra, ain't reaching a wood boiler that is installed outside.
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  9. #9
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    Quote Originally Posted by beenthere View Post
    The sensors of the Ultra, ain't reaching a wood boiler that is installed outside.
    I haven't dealt with WM as much as I have with Lochinvar.

    Lochinvar boilers come with a remote system temp sensor, which you would install in the heating loop, not the injection loop.

    Do the WM not have a remote system sensor? How else can it effectively reset supply temp?

    I am assuming the wood boiler is right in the main heating loop, and the gas boiler is set up as an injection loop into the main heating loop. In this case, you would put the system supply sensor in the main loop, this would let the gas boiler know if the main loop needed heat or not. Kapeesh?

    Again, this is how I am imagining it, because it would minimize pumping energy. The same would apply if the wood boiler is injected into the main heating loop. You would still want the gas boiler system supply sensor in the main heating loop.

  10. #10
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    The Ultra monitors its return and supply temp. And an outdoor sensor. And adjust its temp.

    The heating loop temp doesn't need to be monitored. Since if the reset temp is high enough to heat the house. then the loop temp must be correct.

    Why use a remote, and let the boiler get hotter then needed.
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  11. #11
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    Quote Originally Posted by beenthere View Post
    The Ultra monitors its return and supply temp. And an outdoor sensor. And adjust its temp.

    The heating loop temp doesn't need to be monitored. Since if the reset temp is high enough to heat the house. then the loop temp must be correct.

    Why use a remote, and let the boiler get hotter then needed.
    Plenty of reasons.

    When you use a mod con to heat a home (even as back-up) AND heat domestic hot water, you want it piped as an injection loop, so when the dhw calls all summer long, you only heat the dhw tank and boiler as an isolated system.

    If you gang boilers together, you want the system loop temp, not the temp from each individual boiler.

    Been - look at the hook-up diagrams in the WM manuals, I just did. They use a supply and return sensor in the main loop, NOT the injection loop. They are remote sensors.

    Mod cons are almost always suggested to be primary / secondary. You should sense the secondary loop (heating loop), not the primary, when using OAT reset.

  12. #12
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    Still don't need loop sensors when piped as injection. Even with DHW.

    I only use loop sensors if I'm piping up multiple boilers. And I use the BCP control from WM then.
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  13. #13
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    Well, if you had two heat sources, a gas and wood boiler, and the gas boiler were piped as an injection loop, you would certainly want a system sensor! Otherwise, the back-up gas boiler has no idea if the loop is under load or not! lol

    If you are piping the main loop right through the gas boiler, the dhw hookup would be a compromise, insofar as it would not be isolated in the summer. And, like I said before, you would be needlessly fighting the gas boiler head all the time.

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