Wiring relay to cut heat call during DHW (combi boiler)

[Giantsean]

Hi All,

Thanks for the continued help on this site.. decades of great info!

I have a Navien NCB 240/130H which replaced a CH240. Previously I had it wired up to a time delay DPDT relay so to cut the W wires to two air handlers (upstairs and downstairs) to kill heat calls while we took showers etc in winter. The CH240 was wired per the diagram below (I honestly can't remember why it was so complicated w/ jumpers etc or why it even worked this way… other than I tried multiple combinations to get it to work and I was more of a jacka$$ back then than now )

The new NCB has 2 A/H contacts which close during a heat call, and open when there is a DHW call OR the boiler is not supplying heat. I believe this is normally to open G to cut fan during lack of heat. Using the same relay, is it as simple as wiring a 24v red to "A", and "T" and "B" connect to the A/H contacts? (opening and closing the ground to energize the relay)

Thanks for any advice!

OLD WAY (CH240 circa 2012)

 

[John Gayewski]

I'm not sure on your specific question but those are wired from the factory to prioritize dhw. When there's a call for water heat the space heat won't work. I'm not sure the reason for doing what your doing. Unless of course I'm wrong, but I'm not sure any combi will heat during a domestic call.

 

[Sponsor]

 

[Giantsean]

I'm not sure on your specific question but those are wired from the factory to prioritize dhw. When there's a call for water heat the space heat won't work. I'm not sure the reason for doing what your doing. Unless of course I'm wrong, but I'm not sure any combi will heat during a domestic call.

The boiler turns off the heating... that is fine. However the pumps keep running and the hydro handlers keep blowing unheated air (I should have mentioned it's a hydro setup). What I'm trying to do is cut the whole heat call which will take care of everything.

 

[John Gayewski]

The boiler turns off the heating... that is fine. However the pumps keep running and the hydro handlers keep blowing unheated air (I should have mentioned it's a hydro setup). What I'm trying to do is cut the whole heat call which will take care of everything.

Does the boiler's circulator continue to run during a domestic call?

 

[Giantsean]

Does the boiler's circulator continue to run during a domestic call?

Yes as they are run from the air handler control board. Too many things to shut off individually, but cutting the heat call will take care of all of them

 

[John Gayewski]

So it's blowing latent heat from the system? My understanding of this is that is how it's designed. Stopping everything can (probably won't) crack heat exchangers. Plus I think it improves efficiency.

 

[Fitter30]

Use a flow switch in dhw and a two pole relay to open the W contacts. In series with two wire time delay relays to keep from short cycling boiler.
www.amazon.com/DIGITEN-FS-C02-Thread-Switch-0-220V/dp/B07G77169W/ref=asc_df_B07G77169W?mcid=cac26645e4923218997fdd9f762dc87f&tag=hyprod-20&linkCode=df0&hvadid=693071814664&hvpos=&hvnetw=g&hvrand=15317017609376597170&hvpone=&hvptwo=&hvqmt=&hvdev=t&hvdvcmdl=&hvlocint=&hvlocphy=9023792&hvtargid=pla-804881898155&psc=1

https://www.amazon.com/dp/B0D378TCY3/ref=sspa_dk_detail_4?psc=1&pd_rd_i=B0D378TCY3&pd_rd_w=xAYv7&content-id=amzn1.sym.8c2f9165-8e93-42a1-8313-73d3809141a2&pf_rd_p=8c2f9165-8e93-42a1-8313-73d3809141a2&pf_rd_r=Z23RW1GWFW5SJXZ7ME8B&pd_rd_wg=V5RVi&pd_rd_r=61418d3b-7abb-443b-bf05-73862e1ad91d&s=industrial&sp_csd=d2lkZ2V0TmFtZT1zcF9kZXRhaWw

 

[Giantsean]

No.. air handler during a DHW call. It is still calling for heat, circs are pumping water, but boiler is not making supply heat (because it's busy prioritizing DHW). I know the prioritization is by design, but there is no way now to stop cold air from blowing during showers.

The timer on the relay (90 sec) will take care of the latent heat concern.. it will keep W closed for 90 sec (to avoid abrupt starts/stops, like if we turned on hot water in the sink.

 

[Giantsean]

Use a flow switch in dhw and a two pole relay to open the W contacts. In series with two wire time delay relays to keep from short cycling boiler.
www.amazon.com/DIGITEN-FS-C02-Thread-Switch-0-220V/dp/B07G77169W/ref=asc_df_B07G77169W?mcid=cac26645e4923218997fdd9f762dc87f&tag=hyprod-20&linkCode=df0&hvadid=693071814664&hvpos=&hvnetw=g&hvrand=15317017609376597170&hvpone=&hvptwo=&hvqmt=&hvdev=t&hvdvcmdl=&hvlocint=&hvlocphy=9023792&hvtargid=pla-804881898155&psc=1

https://www.amazon.com/dp/B0D378TCY3/ref=sspa_dk_detail_4?psc=1&pd_rd_i=B0D378TCY3&pd_rd_w=xAYv7&content-id=amzn1.sym.8c2f9165-8e93-42a1-8313-73d3809141a2&pf_rd_p=8c2f9165-8e93-42a1-8313-73d3809141a2&pf_rd_r=Z23RW1GWFW5SJXZ7ME8B&pd_rd_wg=V5RVi&pd_rd_r=61418d3b-7abb-443b-bf05-73862e1ad91d&s=industrial&sp_csd=d2lkZ2V0TmFtZT1zcF9kZXRhaWw

Thanks this is great, but I already have the relay (w/ timer) and the ability to trigger it via those terminals on the boiler (plus no need to open the system to install fittings.

What I need is advice on the best way to wire it. Here's what I have to work with (and sorry.. I thought I already posted this pic)

 

[Fitter30]

Just wire the contacts in series with w from t stats. Contacts on boiler T-T just need a dry contact to bring boiler on.

 

[Giantsean]

This ended up working, EXCEPT for some reason it only works if outdoor reset is disabled. Otherwise the boiler supply temp remains low, even though it seems to respond to the heat call ok, it never fires up completely.

 

[Fitter30]

This ended up working, EXCEPT for some reason it only works if outdoor reset is disabled. Otherwise the boiler supply temp remains low, even though it seems to respond to the heat call ok, it never fires up completel

Page 103 7.1 fan coil. Why is there a red wire from AC24 vl to relay terminal A?

https://www.google.com/url?q=https://fwwebbimage.fwwebb.com/ProductInfo/NCB-H_Installation_%26_Operation_Manual_EN_201130.pdf&sa=U&ved=2ahUKEwjI2pHOtr6LAxWY5MkDHZJpJ1MQFnoECAsQAg&usg=AOvVaw0yE9AgvH3CzDSX3RJcjHo8

 

[Giantsean]

The relay needs A energized with constant 24v to work at all, with T switched 24v to trigger the timer to open or close the upper terminals. I assume AC24VN works as a ground/common for that terminal, but I was still a little nervous hooking it up that way.