I had a Navien NCB-180E Combi Boiler installed several years ago. Recently problems have developed with overheating combustion chamber, error code 001, and shutdown. The professional installer replaced the circulator pump in the unit as indicated by Navien customer support. The problem resolved temporarily but after less than 12 hours, overheated with same error code 001 and reboot. I now can only use the hydronic heat side of the combi unit and not the domestic hot water side. In researching the installation, I noticed the installer (a professional HVAC business) did not follow the installation instructions to use a primary manifold or create a recirculating loop in the domestic heat side of the unit. Now dealing with expensive repair and trying to determine if installation could be responsible for the malfunction and need to repair and replace parts.