Navien NCB 240/110H Not Heating DHW to Temp & Slow to Get Hot Water

[binman]

Hi all, as the title suggests I recently had a NCB 240/110H installed with an external Grundfos Comfort PM circulator pump (circled in image).

When we first installed it, the hot water seemed instant and HOT. DHW temp set at 130F. Scalding within 10-15 seconds at every tap in the house.

Then out of nowhere it seems like we are 4-5 minutes to get even lukewarm water. I set the DHW to 140F and that did nothing in terms of heat.

I changed the external pump as I thought it might be faulty, but nothing. The boiler is flashing DHW between 103F and 128F almost like it is pulsing and not reaching temperature. Something is definitely wrong somewhere.

I am unfortunately dealing with a plumber who isn't familiar with the boiler, and HVAC tech who isn't familiar with the pump, so getting them to coordinate has been a nightmare.

Does anyone know the proper recommended settings on the NCB for CONSTANT recirculation of hot water? Or can anyone see something astray in the pic of my setup. Right now I have it set for external circulation, aquastat, always on - but I feel like I've tried every setting and I all I am getting is lukewarm water slowly.

Thanks in advance,

binman

P.S. I have cleaned the filter in the boiler, that is not the issue.

 

[Fitter30]

Page 109. Brand and model of pump? Pump have a built in check? What is the gpm flow with the recir pump? Has the unit been cleaned with vinegar?

www.manualslib.com/manual/2094574/Navien-Ncb-190-060h.html?page=109#manual

 

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[Bannerman]

What you describe are common issues with Navien NPE tankless water heaters when the unit's internal check valve does not fully close. This leads me to suspect your Navien NCB may be equipped with a similar check valve.

A stuck open check valve will typically allow incoming cold water, or the cooler recirculation return flow, to mix with the hot water exiting from the heat exchanger. This then will reduce the temperature of the hot water supplied to the home's fixtures, and will often also provide an alternate internal recirculation path instead of all DHW being forced to recirculate throughout the home's plumbing lines.

A stuck open check valve will also cause the internal DHW flow meter to sense a lower incoming water flow rate, thereby resulting in a reduced DHW heating output compared when all incoming flow is passing through the flow meter.

 

[binman]

What you describe are common issues with Navien NPE tankless water heaters when the unit's internal check valve does not fully close. This leads me to suspect your Navien NCB may be equipped with a similar check valve.

A stuck open check valve will typically allow incoming cold water, or the cooler recirculation return flow, to mix with the hot water exiting from the heat exchanger. This then will reduce the temperature of the hot water supplied to the home's fixtures, and will often also provide an alternate internal recirculation path instead of all DHW being forced to recirculate throughout the home's plumbing lines.

A stuck open check valve will also cause the internal DHW flow meter to sense a lower incoming water flow rate, thereby resulting in a reduced DHW heating output compared when all incoming flow is passing through the flow meter.

I had the check valve replaced this morning. Hoping this suffices. What do you recommend my DHW recirculation settings be set to for an external Grundfos Comfort PM recirc pump? No recirc, external recirc, or combi pre-heat?