Navien recirculation

[MikeO411]

I recently added a Navien NCB combi-boiler beside my existing NPE-A water heater. Prior to this I had the dip switches on the NPE set to the intelligent preheating mode and the re circulation system worked wonderfully. Since linking to the NCB, i had to set the NCB as the master and the NPE as the slave, the re circulation has stopped and I can not figure out what settings or dip switch changes I need to make to get this feature working again.

Can anyone help me with this?

 

[Bannerman]

First off, the installation must be plumbed slightly differently for recirculation to work in a cascaded system. Page 34 of the NCB-E Installation Manual, shows a check valve is to be installed in the incoming cold feed line to the NPE device, and a 120 VAC normally closed solenoid valve is to be installed in the hot line leading from the NCB-E unit. You didn't specify if those were installed.

https://www.navieninc.com/products/ncb-240e/downloads

 

[Sponsor]

 

[MikeO411]

First off, the installation must be plumbed slightly differently for recirculation to work in a cascaded system. Page 34 of the NCB-E Installation Manual, shows a check valve is to be installed in the incoming cold feed line to the NPE device, and a 120 VAC normally closed solenoid valve is to be installed in the hot line leading from the NCB-E unit. You didn't specify if those were installed.

https://www.navieninc.com/products/ncb-240e/downloads

Thanks for the reply. Yes, there is a 120 VAC normally closed solenoid valve on the on the NCB combi-boiler DHW supply line. There a re-circulation return line from the last fixture to the NPE unit. This plumbing configuration works well for re-circulation when not in master/slave mode, but I'm not sure the NCB will ever heat DHW this way since there is no flow due to the NC valve?? When linked, there is no re-circulation in the intelligent mode, but hte NCB does heat DHW when demand is there. I'm thinking the intelligent mode might not be supported when linked? I did not find any documentation for DIP switch setting in this configuration.

 

[Bannerman]

I'm thinking the intelligent mode might not be supported when linked?

Page 45 of the NPE installation manual states Intelligent Mode does not function while in Cascade Mode. Page 45 shows the settings for each DIP switch.

I think the NC solenoid valve at the combi-boiler will prevent the NCB from providing heat only while DHW recirculation is needed. Recirculation should not usually require much heat, probably much less than the minimum BTU output from one heating device. As such, it seems only the NPE-A will supply hot water for recirculation as that is the device equipped with a DHW buffer tank and internal recirculation pump.

 

[MikeO411]

This was helpful, thanks for the reply.