Navien NFB 200

ahelwig

Hello. I have a NFB 200 that I use for a snow melt system (virtually the same as a radiant heating system but outside). Havent used it yet, we finished the house in the spring of this year. Getting ready for our first snowfall so getting used to the system. The question I have has to do with the boiler when I have all the pumps off so no zones are calling for heat. I notice that the boiler will run from time to time anyways. I can tell by the exhaust (see it in the cold weather) as well as the condinsate line. I would expect this when I am calling for heat in either of my two zones but not when I am not calling for heat. Can someone explain why this might be hamening and if there is any way I can stop it. Seems like a waste of energy. I may have the boiler on for a month just sitting waiting for the sensors to tell it to run hot water the zones. Seems sill that it would be using gas for that month while just sitting. I have been just powering it off while not in use but that also seems silly to me that I have an automated system but have to manually go turn on the boiler when I think I may need it

rick in Alaska

I am not familiar enough with that unit, but am wondering if it has a built in protection that when the temperature falls to a certain point outside, that it comes on once in a while to keep itself from freezing up. I know quite a few of them have a heating pad on the back of the heat exchanger for this, but it seems to me that a few of them also have a second level of protection if it gets too cold. Also, it might just have a built in exercise program where it just runs itself for a bit just to keep things from seizing up from sitting.
Rick

Ironman

It really depends upon how the boiler and SIM controls are setup for your particular situation.

Depending upon which SIM control that you have, it may be set to “idle” which means that as the outdoor temp gets near 32*, the control will begin to slightly warm the slab in anticipation of snow even though there may be none yet.

ahelwig

Thanks. I actually dont have the outside sensor connected. When looking at the display it shows the outside temp at --. The units are set in my foam insulated garage and the temp doesn't fall below 50 degrees.

Ironman

I’m referring to the sensor for the SIM control, not the boiler’s outdoor sensor.

jinbtown

couple possibilities I can think of?:
cold temp exercising, my Lochinvar runs the pumps below 45 and the boiler fires below like 38 or something, but iirc my Loch looks at return water temps to make this judgment
your snow melt system is prewarming the slab, if it's automated it may use precipitation or temperature as a predictor
your system is set up with a heat exchanger or a buffer tank and the boiler is controlled by an aquastat vs being controlled by the snowmelt system directly, aka the temperature of the buffer tank or heat exchanger falls below 75F and the system comes on to keep that fluid at a certain temp, then snowmelt system circulates glycol through that heat exchanger and out to the driveway, and that pump only runs when called for