Call for DHW, but Navien NHB-150 burner does not turn on

[Mev]

We had the logic board replaced on our NHB-150. I set the parameters back to what I had for a custom curve using the outdoor temperature sensor. Heating the baseboards has been working fine, but today I noticed that the burner was not running when the DHW was calling for heat. The Taco SR506-4 controller was not changed, priority for zone 6 was still on so the boiler would first heat up the hot water tank.
My installer is in the hospital, so he told me to call Navien support, but they won't talk to me about changing settings.
I turn off the outdoor sensor and the burner starts up, supply temp ramps up to 165, and the hot water tank heats up. I turn the outdoor sensor parameter back on and the burner shuts off while the zone pump keeps pumping water into the hot water tank.

I had a picture of the dip switches from the old logic board and they are the same on the new board. I also verified that he wired up everything the same as before.

Does anyone know what parameter I might be missing?

Oh, just out of curiosity, what does CH stand for in "Current CH demand status"?

Thanks,
Mark

 

[Mev]

I talked to Navien. The outdoor reset curve will control the supply temperature when the DHW is calling for heat. Since my curve ended up with a max supply temp of 104 degrees at 60 degrees outside temperature, the burner would not turn on when the water heater's temperature dropped below its 130 degree set temperature and outside it was 63. It would just keep circulating without running the burner. Today it is around 43 degrees out and the hot water tank temperature dropped to 115, the burner came on but stopped when the supply temp hit 125.
Navien said there is nothing I can do except turn off the outdoor reset control.
I can keep changing these parameters depending on the seasonal temperatures, multiple times a year. Don't mind doing this, but most people would not want to do this. There must be another solution. Flatten out my outdoor reset curve, but would that lead to short cycling during spring and fall? Oh, I'm in north Massachusetts.

 

[Sponsor]

 

[Arseniy M]

Is you DHW tank set up as an extra zone (not as specified in the NHB manual) or off the stub-outs on the primary loop? How is the DHW pump wired? Are you using their manifold? ODR sensor should play no part in DHW temperature. CH stands for Central Heating.

 

[David Philips]

I realize this is too late for the OP, but I came across this thread while searching and thought this might be helpful for others with this problem. I had the same issue with my install (Navien NHB-80, Superstor Ultra 45 indirect, Taco zone relay, and three Taco 007-F5 circulators: two heat zones + indirect zone).

The problem was that the DHW aquastat and circulator were wired to the Taco relay and not the Navien boiler. When the DHW called for heat, the aquastat would signal to the Taco relay, which would power the zone circulator and signal the boiler via the boiler's TT input. Since the boiler had no way of knowing whether a call was coming from the DHW or a heat zone it would apply the ODR curve and the indirect would never reach temp - needless to say you can't heat water in an indirect to 140º by pumping 100º water through the coil.

The fix for this was to move the wiring for the DHW aquastat and circulator from the Taco relay to the correct headers on the boiler. Now the boiler knows the difference between the DHW/aquastat and a heat zone thermostat call from the Taco relay; when the DHW aquastat calls for heat the boiler ramps up to the DHW set point regardless of the ODR curve (and a "DHW" indicator is displayed on the boiler front panel). The boiler then needed to be set to power the boiler pump during DHW calls.

This does still leave the issue of no DHW priority. Since the Taco relay now doesn't know when the DHW is running, when a heat zone calls while the DHW is heating that heat zone will also get water from the boiler at the DHW setpoint. I haven't addressed this yet, but I think the simplest way is to pigtail the aquastat from the boiler so that aquastat signal can also run to the priority TT input on the Taco relay (note the DHW circulator would still only be wired to the boiler). This way the Taco relay will know when the DHW is calling for heat and not power the heat zone circulators until the DHW is satisfied.

Actually, I just realized that if I'd done something like this in the first place - connecting the aquastat to both the Taco relay and the boiler - I could have avoided moving the DHW circulator wiring to the boiler.

Aside from that, I don't know if using the Navien smart relay instead of the Taco relay would allow wiring the DHW only to the relay as was done originally. I'm wondering if the Navien relay's additional data link to the boiler would allow the relay to tell the boiler whether a heat zone or DHW was calling. I'm guessing the Navien relay manual could tell me.

 

[Fitter30]

On taco taco control is there a jumper between zc-zr or x-zc? Terminal strip cn 12 t-t are wires land on termials from taco control? Dip switch 3 on the board is it off? In set up DHW priority time set for 40-60 minutes?

 

[David Philips]

On taco taco control is there a jumper between zc-zr or x-zc? Terminal strip cn 12 t-t are wires land on termials from taco control? Dip switch 3 on the board is it off? In set up DHW priority time set for 40-60 minutes?

Taco relay has jumper between zc-zr.

Boiler cn10 (TT/ CH) is connected to Taco isolated end switch (X, X).

Boiler cn12 (TT / DHW) is not connected to Taco (indirect aquastat is connected directly here). Adding a connection between this and the Taco priority zone TT (while keeping the aquastat connected to cn12) was my planned next step.

Boiler DIP SW3 is off.

Boiler DHW priority time set to 30 minutes - but since the only circulator under boiler control (other than the boiler pump) currently is the DHW circ, this doesn't matter correct?

Also, to clarify, so far I've had no issues with DHW supply. My desire to get DHW priority working is only to prevent the hotter water from going through the heating zones if they call at the same time (my ODR is set to never get the heat zone water up as high as the DHW setpoint).

 

[Fitter30]

Taco when dhw calls its pump should turn on, other zone pumps shut off. Boiler ch12 needs a input either when its pump turns on a aux contact closes powered by a 120volt relay from pump power or a flow switch to prove flow. To test it make dhw call for heat its pump comes on jumper ch12 see where your boiler temp runs.

 

[David Philips]

This does still leave the issue of no DHW priority. Since the Taco relay now doesn't know when the DHW is running, when a heat zone calls while the DHW is heating that heat zone will also get water from the boiler at the DHW setpoint. I haven't addressed this yet, but I think the simplest way is to pigtail the aquastat from the boiler so that aquastat signal can also run to the priority TT input on the Taco relay (note the DHW circulator would still only be wired to the boiler). This way the Taco relay will know when the DHW is calling for heat and not power the heat zone circulators until the DHW is satisfied.

I spliced the aquastat line so it runs to both the boiler CN12 and to the Taco relay priority zone TT. Now the Taco relay knows to not run the other zone circs when the DHW is calling. When the DHW is satisfied, circulators for calling zones are powered and boiler temp drops back down to ODR setpoint.