Navien NHB Series Boiler - Error Code 291

[ShawnW123]

I have a Navien NHB series boiler that produces an error code 291 about 5 minutes into its call for heat.

Boiler fires, pump activates, hot water begins to flow and the temp readout gets to 104 (which is the setting for this unit as it is heating a cement garage slab).

I spoke to a Navien tech who first said the error code didn't exist and then caught himself on further research. He made mention that the supply temp and the return temp sensor maybe reversed.

Can someone explain this.

You friend in northern Minnesota.

PS: On further review the boiler did not come with supply and return temp sensors. Purchase two, install and done? Thanks again for helping me on this. We're out at the end of the GFT. Makes troubleshooting a bit harder.

 

[Fitter30]

E 291 supply/ return inversion temperature
return temp higher that supply temp by +10*
Since boiler has been running fine supply or return sensor could be failing .
Main board cn29 supply, cn30 return sensors
Check connections, fire boiler watch sensor temps
Sensors usually sold in match pairs