Navien combi boiler running continuously

mh330

Have a Navien NCB 180E combi boiler installed. Its producing hydronic heat run to an air handler as well as DHW. However, i realized that when i set my thermostat to "fan on" with the system set to "off" just to circulate some air, the Navien is kicking on and sending hot water to the blower to maintain its min temp of 140. Asked support and they said to make sure dipswitch #7 is set to down for zoned heating which it is. So i have 2 concerns:
1. When summer comes and i want to use my a/c (which uses the same air handler) will the navien continue to send 140 degree water to the air handler and fight my a/c? Its too cold now for me to turn my thermostat to "cool" and try it out to see what the navien will do, as i don't want to stress my condensor.
2. Is the navien supposed to hold water constantly at 140 in a sort of "standby" mode waiting for the thermostat to request hot water to the air handler, and does that mean i'm wasting fuel? When i do set the thermostat to "heat" the navien maintains the circulating water at 140 so this is its normal heat/operating temp.
Anyone know why my Navien seems to be set to "always on" hydronic heat and how to get it into a "standby" mode?

Thank you!

Rich_49

What air handler do you possess that REQUIRES 140* SWTs ? Heat transfer will take place until everything is EQUAL . I have many HVAC (lol) friends who swore you needed that temp water and have since learned that 140* is the highest they need during colder temps and that 100* water is plenty sufficient at higher outdoor temps .

The summer should not be an issue if the Outdoor sensor is installed and WWSD programmed .

mh330

I don't know that it requires 140 degrees, that's just what the Navien default setting is (as far as i know).

Don't have an outdoor sensor installed.

Teemok

The thermostats G terminal is what sends voltage to activate the fan only. How your system is wired is the issue. Most air handlers have a G terminal that just turns on the fan only. How the pump is activated and how the boiler is called to for heat needs to be checked for good logic.

Rich_49

mh330 said:

I don't know that it requires 140 degrees, that's just what the Navien default setting is (as far as i know).

Don't have an outdoor sensor installed.

Well get that installed asap . That boiler and others like it ( mod cons ) are pointless in the grand scheme of things , without it