Remove Mixing Valve and Mixing Valve Transformer and flush unit to ensure no sediment is built up. Arrived after Markus installed parts, tested and there were leaks. Fixed all the issues and the unit had the same error, called Navien and they recommend new valve that we installed. Will return with new parts. Technicians returned to install new mixing valve. After installation the error code e045 still appeared. Technician called navian to troubleshoot. Navient representative clarified which mixing valve was the problem and stated it was not the one we had replaced. technicians called local supply house to see when it would be available and they stated the following morning. Technician set up new appointment for the following afternoon to install proper part. Technicians removed newly installed mixing valve and replace the original mixing valve that is in proper operational order. Technicians called dispatch to schedule new call. Technicians cleaned work area and left.