Navien NCB 250-110H Wiring to suntherm air handlers.

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Morrelli

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Hello all, I have posted a few times and hoping for some help. Recently had a Navien NCB 250-110H installed in place of a very old water heater that feeds two suntherm air handlers and DHW. AH model numbers and faded wiring diagram below. The combi navien has three zones, the handlers have their own pumps. The installer wired it such that the navien circulates a small loop at the unit that holds at 140 degrees and when one of the handlers calls for heat, its check valve opens, the navien senses circulation and drives temp to 180 to circulate through handler. He did not use the zone connections at the navien, instead he has a 24 volt transformer with an on/off switch for the heat side. Well, this seems a waste of propane to me. i would think each handler should be on its own zone. the navien should be more than capable to get to 180 when either handler calls for heat, not to mention having to turn a switch on and off for heat season to avoid a cycling 140 degree standby. in looking at the schematic, hoping to get a more clear one from suntherm, can anyone tell me which wires on the handlers should be connected to the zone terminals,(two conductors for each zone output), on the navien? As mentioned, the air handlers have their own pumps so having a pump running at the navien circulating a small 140 degree loop and then getting a call for heat from the handlers make me wonder if the pumps might be "fighting" eachother. Any help appreciated. I really need to make sure this is as efficient as it should be and that the controls/ navien programming are correct. Air Handler Model number:H15-52-52-A1B-CPIX-CA048A895-B2
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Fitter30

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Need some pics of boiler piping around the boiler and going out to air handlers.On the main board cnt3 is their a sensor wired to it? Smaller board cnd1 dhw priority & air handler. Dhw where do the wires go? Air handler if there are wires where do they go? Take some pics of both boards terminal strips want to know what has wires on them. Safe site been using them for years.
 
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Morrelli

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Tried my best, very very tight space. The yellow lines on the insulated piping lead to both air handlers. The switch and transformer send 24vdc to t/s zone 1, supposedly keeping standby 140 degrees for tstat call from either handler..no sensors/connections connected to any of your asks. Pics of both boards. Pleaae let me know if you need something different/more. thanks.
 

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Morrelli

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one more...pupes to air gandkera running under "switch"
 

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Fitter30

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Here's the correct install manual
Pages 103 & 104 tell how to set minimum water temp down boiler side. Write down all changes made.
Looking at the air handler wiring diagram can't read the relay number it's above the transformer left. The coil looks like white and yellow feed the coil. By parallel the coil with a added relay the contacts will run to boiler terminal strip cnc4 and cnc5 left and center terminals. Do the the air handler thermostats have a off position?
By adding a outdoor air sensor to cnt 3 north side of house this would give u outdoor reset and outdoor temp shut down - boiler. Pics of piping couldn't follow the piping but this should help.
 

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The tstats for the handlers are just honeywell 9000 wifi stats with system on/off, heat/cool. I am not knowlegable as for controls, but it sounds like you are suggesting a relay picking up coil power from the same relay on the handler that puts the handler in heat cycle when called for from tstat? On the outdoor reset sensor, does this sense temperature to control the constant circulating versus on demand? In other words, it automatically controls the small heated loop at the unit based on outside temps and usage so i dont have to manually flip a switch as it as now? Sorry, just trying to wrap my head around it. Are better pictures of piping needed? Ill try to post a better AH schematic as well. Thanks again!
 

Fitter30

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The two air handlers thermostats when either turned to heat and calling will turn on the boiler side. Out door sensor will do two things with programming keep boiler from running above a certain outdoor temp and will vary the boiler side temp. If the reset program was 100° at 70° outdoor and 170° at 0° outside.
Thermostat wire can be run from each air handler added relay n.o. contact to boiler.
 

Morrelli

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really appreciate the help. Im still a little stuck on the outdoor reset. " Out door sensor will do two things with programming keep boiler from running above a certain outdoor temp and will vary the boiler side temp." I understand not wanting the boiler on when its warm outside. But, when it's cold outside, is it more effficient to have a "side" temp ( which i think i have been referring to as standy circulation at boiler) rather than just calling for heat from a stone cold boiler? LP is very expensive here so just trying to balance cost against comfort a little. Typical winter temps may get down to 25F, but are typically mid 30's. my thinking is that calling for heat without any side ( or standy circulation ) would maybe take a bit more gas than just keeping it at 100 degrees with the modulating ability? More importantly it reduces short cycling of the boiler? Maybe reduce condensation as well? Again, thank for your support, it is very much appreciated!
 

Fitter30

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By having a variable water temp based on outside temp is more efficient. Burner temp not hot enough will never get a room temp satisfied. One that is too large will drive the temp up to fast possibly over shoot the setpoint of t stat then the room temp drops and refires boiler. Boilers are more efficient with a longer burn time. Look at pages 114 & 115 their are lots of adjustments for the burner.
 

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fitter30, I'm confused again...if i parallel off that relay, does that mean i need an additional relay for each handler so it can differentiate which handler is being called for heat? one for cnc4 and one for cnc5 zones?
 

Morrelli

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So installer came back. Picked 24v off relay at AH's and wired to zones 1 and 2 at combi. All works fine, but when call for heat from t-stat ends, AH's immediately stop. That leaves hot water in coils and time delay relay at handlers disabled. Question: Can wiring from T-stats go directly to combi first, then to AH's so the time delay relay function at the AH's will function and utilize remaining heat in cycle?
 
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