How do you troubleshoot when the pump won't prime and start the water flow?

The suction line needs to be filled with water via the priming port. Make sure that all plumbing connections are tight, including the threaded union located above the check valve. Any air leaks in one of these connections can prevent the pump from priming properly. Make sure the check valve is free and clear of debris and is in a vertical position that allows the internal flapper to seal and hold the water in the pipe when the pump is not operating.

Note: If the initial attempt to prime the pump fails, you must turn off the pump and allow it to cool down for a few minutes before attempting to prime again. This prevents the risk of damaging the mechanical seals through thermal shock during another priming attempt (suddenly introducing cold water to the warm mechanical seal surface).