Navien NHB-150 or the Thermostat or Both

newinnj

hi,

I was about to replace a thermostat and the better half asked some questions and then she gave me a quizzical look so I decided to get smart and post this.

This winter season in the very early morning I have seen the supply side temperature go out as high as 176. The Navien NHB-150 heat load setting is set to 4 - Low Mass Radiant which is about 140 on the max side. Now with the warmer temperature about the 30's the walkout basement hit 76 degrees when it was set to 72. I checked the boiler and that zone was the only one calling for heat and the boiler was putting out 170 degree supply side water. I turned off the thermostat. The call for heat stopped the boiler shut down and eventually the actuator closed up. My initial reaction was the old thermostat (White-Rodgers) about 2003 model basic one was not working correctly. However I thought the boiler should be smart enough to have a call for heat and monitor the temperature so it might be continually running but not have just a hight temperature. Basically the pumps will be running and continually circulate water at low temp.

Do I have a thermostat and or boiler issue?

White Rodgers - Model 1F78 non programable (2003)

Navien NHB-150 Boiler

Taco ZVC406 zone controller.

5 zones and 3 thermostats (All white-dodgers same year)

Sub basement - no need for heat since the boiler pipes gives it enough heat and very small space. Thermostat off and valve turned off. It is concrete floor and I didn't want the warmer wood floor temps to go the concrete floor. Also did not need the heat. (Thanks for the advice on that one).

Walk out basement - Problem described above. One thermostat and one zone

main floor - One thermostat and three zones.

Apologize in advance if I did not use the correct tech terms etc. I will provide any pics or more info.

Jamie Hall

That boiler has — or should have — an outdoor reset which adjusts the boiler water temperature in relation to the outdoor temperature. That's fine — but what it can't know is how many zones are calling all at once. So if you only have one zone calling, such as your example, it will still put out water hot enough to serve all the zones.

Now what should happen, though, if only one zone is calling (as in this case) is that it may cycle on and off — but the thermostat should turn the whole show off when it is satisfied. And in this case it sounds very much that the thermostat is the problem…

newinnj

Thanks I agree Jamie, I have a Honeywell Home Pro 3000 series ready to go.

What is puzzling to me is the boiler has the water supply side temp going out and the return temp coming in and working with the outdoor reset should it be smart enough to regulate the water temp? I am worried I actually might have two issues and the second with the boiler itself. In the initial install the boiler circuit board was replaced for another issue and wondering if I have a continuation of the story with this boiler.

Jamie Hall

You might. I'd replace the thermostat first, though, particularly since you have it, and then worry about the boiler. It may be that the reset curve isn't right.

JMWHVAC

If the boost function is enabled the boiler water temp will eventually reach max if there is a continual heat call for a long enough time. The time is also adjustable.

pedmec

Make sure that the outdoor sensor is connected. If the sensor is not connected it will default to the factory settings. Check the target temperature when its running. You should be able to see the target temperature. if the target temperature is say 170 with a 6 degree offset and 12 degree differential then it is doing what its supposed to.

newinnj

Gents thanks you solved it.

Thermostat replaced. Heat call was made.

Outdoor sensor was connected and has been working with reset function on.

The boost function is a prime suspect. It was set and duration of time was 30 minutes. It has been turned off. On the overnight there will be a rapid drop in temperature around 5am it's going to be 16 degrees. Everything makes sense now! Factory default setting is off. So something happened and it could have been me. 🤐

I will monitor for several days and report back.

newinnj

It looks like the surge of hot water is over with the boost off. The thermostat is working fine.

This uncovered a new "old" problem.

The new setup with boost off the house now is colder. Walkout basement set at 72 is now 68 and main floor is set to 72 and is now 70. The reason is that the boiler can't keep the house warm. The root cause I think is this.

I live in a walk up and I am on the ground unit. Not many places to put the outdoor sensor so it's attached to the garage door trim. The entire garage is below grade and by nature is it warmer than the outside temp. I knew it can be off by a few degrees. Right now it's at 34 and sensor is at 32. However the colder it gets the difference is greater. 16 degrees Sunday morning but the sensor read 28 degrees.

If you all agree with that being an explanation then the question is what is worse putting very hot temp (168) to the wood floors or live with the colder temperatures in the house. The house temp will move up and down especially in the cold weather. Unless there are configurations on the other parameters that can take into account of the sensor not being accurate in cold weather. If the recommendation is to put the boost back on should it be set to 30 minutes or another time range?

Thanks for all of the help.

I will open up another thread on another item I am seeing with the boiler.

Jamie Hall

Now that's an interesting problem. Surely there is a window or something somewhere where you could put the outdoor sensor? May involve running some wire… the preference is on the north side, shaded — but seems to me that maybe you could contrive a sort of arm from a window frame, perhaps, with a shade over the sensor?

Hmm…

newinnj

I live in a condo. Limitations on what to do. The nearest window is the south side. A ton of sun. I will have to go up another floor and then it gets tricky with the window.

I am throwing some ideas out there.

Option A

Keep the low mass radiant setting. Keep the boost off.

Parameter setting

Lowest outdoor temperature: "This mode is used to configure the lowest outdoor temp. The boiler will operate at the high end of the supply or return set point range at this outdoor temperature" ==Potentially set this at 30 degrees Fahrenheit. Default is 14 degrees.

Option B

Keep the low mass radiant setting. Keep the boost on. Hot water to the wood floors.

Option C

Keep the low mass radiant setting. keep the boost off. There will be some days colder in the house than others. No hot water to the floors.

Option D

Not an option. Change the low mass setting to custom. There are four temperature setting for min max supply and return side temps. But back to the same problem. Temp in the house is cold and if boost is on it will override the custom temp setting.

newinnj

Jamie Hall

I really don't like the idea of hot water in the radiant floors. Pretty hard on the wood…

Your Option A may work. There is some flexibility in the outdoor reset "curve" settings, but it's going to be a bit tedious. One suggestion, though… if you do get that to work, write down what the settings are that make it work, and why they are that way, for future reference!

newinnj

At this time the boost is off. The minimum outdoor temp default was 14 and I moved it to 38. That temp is about where the temps between the real temperature and the sensor temperature starts going off in different directions. At this time the hot water max is about 140 which is the high end of the low mass range when the temperature outside gets real cold. Most times the water is not that hot and runs sometimes around 110 etc. The house is warm. I checked every setting and every setting is at the default setting except for one. The DHW pump is off when using heat. I have indirect tank and I did not want the colder floor water to cool down the indirect. I hope that is ok?

One item left and I think that will be a different thread. How to fine tune an oversized boiler.