NFB 175H Thermostat

bscott13 · September 19

I recently had an NFB 175H boiler installed along with an indirect water heater. My question is about the installation: the installer connected the indirect water heater thermostat to zone three instead of using the dedicated DHW block. Zones one and two are used for my baseboard radiant heat. When I asked why it was done this way, the installer responded, “We prefer to pipe it as a heating zone because it simplifies troubleshooting in the future. We could have piped it directly off the manifold, but that can make it harder to diagnose a failure of the primary pump. That’s why we did it this way.” Does this make sense?

109A_5 · September 19

Well, is seems it is more than just moving the two wires in your annotation, but not enough to avoid it. How does the boiler (or the system) control the water flow through the indirect water heater ?

IMO doing it the way they seemed to have installed it (can't see the whole DHW loop in your pictures) you are loosing out of features the boiler has built in like DHW priority and maybe DHW temperature control by the boiler's user interface.

I'm not sure I buy their explanation. So for ease of their (maybe future) troubleshooting you loose features and functionality, seems lame to me. They could close the isolation valves to the indirect water heater if that is messing up their troubleshooting strategy.

Kind of seems like it is not piped per the instruction manual either (however I did not read the whole manual).

109A_5 · September 20

Sorry, I did not see you added a picture, it seems Edits don't push the thread to the top of the queue or trigger notifications.

It looks like they used a Zone Valve instead of a circulator for the DHW zone. Maybe a cost savings strategy on their part. If I understood the manual correctly. The way I believe the boiler is set up electrically (and logically) if you use the DHW thermostat input you need a DHW circulator. Since I suspect the boiler will not turn on the "Boiler Pump" or the "System Pump" circulators, it wants to turn on the "DHW Pump" circulator. (there are ways around that, but that just complicates things)

It looks like the way they piped and configured the system, for you to have DHW the Boiler Pump AND the Zone 3 Pump (System) both have to be running and the DHW zone valve needs to be open. It may work but you probably loose the DHW priority and maybe other features and you are powering an extra circulator and a zone valve for your DHW.

I would venture to say that is not what Navien intended.

It seems when the DHW thermostat input is used it is the same as Zone 1 but with different features / functionality for DHW service.

As far as troubleshooting (at least from a newcomers point of view) If you build the system different from what the manual shows that may add confusion, not making troubleshooting easier. Like a "not enough DHW" complaint in the middle of the Winter.

JMWHVAC · 1:44AM

No, their explanation doesn't make sense, and I still wonder, WHY would you do it that way? Do they have outdoor reset activated? If the settings are done right it will work but it is not the normal way of doing it. BTW, a good boiler you got there.

109A_5 · 4:50AM

https://forum.heatinghelp.com/discussion/comment/1865553#Comment_1865553

" WHY would you do it that way? " The only thing I can come up with save the cost of a circulator. And they were not even consistent with the placement of the Zone Valves.

Made me think of something else, WWSD (Warm Weather Shut Down) Probably disabled. Another lost feature.

No DHW above a WWSD set temp. Sadly too funny. Probably still disabled.

If the Outdoor reset was enabled it may provide poor DHW temperature or extended boiler run time since the indirect's thermostat may never be satisfied. Since the boiler thinks it is a normal heating zone.

In this case, many pitfalls when you don't follow the manual. If you follow the manual and then if it does not work correctly it is not on you.

bscott13 · 6:53PM

Thank you, I appreciate your thoughtful review and comments. It sounds like the installation wasn’t done according to the manual’s specifications. I am not sure where to go from here or if it’s worth pursuing a change.

109A_5 · 9:39PM

Few paths you could entertain.

If you have not, you could read all the documentation so you understand your new boiler and all its features better. I'm not sure what your contractor obligated themselves to supply and install.

You could see how it performs as is, DHW performance (especially when it gets cold out), fuel bills etc. If it falls short of expectations you now have a clue why. Is there a warranty on their install and for how long ?

If the features like Outdoor Reset and WWSD (Warm Weather Shut Down) sound like features you would enjoy using and you enable them, monitor the performance, if it fall short complain.

Maybe a bit late in this season for WWSD (Warm Weather Shut Down) activity but I bet if it was enabled, and is set for 70 degrees and it goes above 70 degrees outside you would loose the DHW heating. Maybe they never bothered to install the outdoor temperature sensor.

Have a another contractor look at the situation.

Many folks here on this site do their own work, not sure if that is an option for you.

There are other routes if your not satisfied with the work the contractor did.

NFB 175H Thermostat

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