When performing a water isolation trace in ArcFM Viewer for ArcGIS Engine the message "The trace task returned no elements in its results" is displayed in the status bar of the application. A sequence of errors are also found in the Miner event log. The issue does not occur on a machine running ArcFM Desktop when using the same data and trace.
This is a known bug MM53478, which has been resolved in 10.2.1b. Prior releases can use the workaround below.
Assuming upgrading to 10.2.1b is not in the works already, the bug can be resolved by adding a registry key (attached to this KB article) to the system. This registry key is preset by the ArcFM Desktop installer but not the ArcFM Viewer for ArcGIS Engine installer, and prior to 10.2.1b the key's absence resulted in the isolation trace failing to switch to water mode.
This registry key is stored in the current user section of the registry and so will either need to be added for each user that expects to use the machine, or it can be set for the .Default user in the registry.