Navien CH240 cold on 1 floor only. Fine on other floors.

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macplee

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Just bought this house with the Navien CH240. When outside temp drops to the teens or single digit, the 1st floor could only reach 60-65 max.

Here are more info:
The thermostat works fines
This is a 3 story house with 3 zones (one zone per floor).
Dip switches set to 180 by previous owner/plumber.
One very troubling thing and potential problem I noticed is that one room on the 3rd floor is tied to the first floor zone. But just this one room. The plumber won't believe me and tells me that even if that was the case, 1st floor zone should still heat just fine. But I read somewhere about split loop and how the hot water could be going to the path of least resistance and could potentially loop around that path (3rd floor). I am afraid that split loop path may be the 3rd floor room that's tied to the 1st floor because that room stays nice and warm even when the 3rd floor zone is turned off.

Also notice the dip switch #4 is not up or down, but kind of in the middle. Figured I would get some advice first before I touch anything.

Any help? The plumber who installed this system is extremely unresponsive.
 

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Dana

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The CH240 is ridiculously oversized for almost every house in MA smaller than 8,000 square feet, so if there's enough radiation to emit the heat into the first floor with 180F water, it won't much matter if it's splitting it's flow to other places. The difference in radiator output at 0.5 gpm isn't hugely different from it's output at 5.0 gpm.

If the oddball third floor room is tied in to the first floor in a parallel loop it could be taking the lion's share of the flow. There should be a ball valve or two for balancing the flow it's it's split off in parallel rather than in series with the rest of the rooms on that zone.

It's a bit silly to have a condensing boiler running at 180F, and thus never condensing, but it may be constrained to always run at high temp if it has insufficient zone radiation to keep from short-cycling when the water temps (and heat emittance of the radiation) is lower. If the radiation is fin tube baseboard, it'll deliver about 500 BTU /hr per running foot with an entering water temp (EWT) of 180F, and about 250 BTU/ft-hr at an EWT of 130F, where it'll be edging into the condensing zone. The min-fire input to the thing is about 20,000 BTU/hr, which at condensing temps is about 19,000 BTU/hr. To not short-cycle in condensing mode you'd need a large fraction of 19,000/250= 76 feet of baseboard on each zone, which you probably don't have (?), which may be why they set it up for a fixed temp 180F, where the output of the boiler would match the output of the radiation with as little as 38' of baseboard.

Go around and add up the radiation sizing/type on each zone separately and report back.

SW2 position 4 is related to the "K-factor" curve when the output temperature is under return temperature control when using the outdoor temperature sensor option. See pages 48, 52 , & 59 of the manual. Any type 4 is "on", the boiler output would be sensing the return water temperature. It's not clear from your photograph if whether that is affecting behavior at all, but by all means verify that it is in the OFF position

From the picture it's obvious that you have an uninsulated fieldstone foundation, with poorly installed joist insulation in the floors, which is increasing the heat load of the first floor more than you might think. In MA they'll usually let you use 2" of closed cell spray polyurethane on fieldstone foundations with only intumescent paint for fire protection, which would make a real difference. Get a MassSave audit, and let the auditor know that you're interested in both air sealing the place as well as insulating the foundation, see if they won't subsidize that. You'll get a lot more bang per buck out of insulating and air sealing the foundation walls & band joist than from stuffing the joists full of fluff, and that alone may make the difference as to whether the first floor zone keeps up when it's cold outside.

A three story house has a large "stack effect" drive, and any air leaks in the foundation or band joist pulls outdoor air into the basement and under the first floor. Sealing the basement is as important as sealing the top of the house (including the top & bottom of plumbing & electrical chases or flue chases that run from the basement to the attic, etc). And every square foot of that uninsulated above-grade brick is losing between 5-10x as much conducted heat as a square foot of above grade wall too, despite the cooler basement temperature.

If you plan on finishing the basement into living space you may want to do something other than a 2" closed cell foam + intumescent paint solution.
 

Tom Sawyer

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Before making a call, I'd like to know how much radiation is being served on the 1st floor. If it's a staple up, radiant job, there most likely isn't enough square footage of radiated floor to keep up with the low temperature. Pretty common mistake made by greedy and over zealous installers.
 
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