Before restarting an HTEC, please inspect to ensure proper shut down procedures were performed.   Most issues dealing with improper storage are related to salt precipitates clogging lines when mobile phase dries out, or bacteria growth,  For proper shutdown of the HTEC-500/510, please see this article.   Signs of leaks or clogging include extremely high or low pressure.  A spike in pressure reading followed by a rapid drop to zero indicates a clog followed by a fitting becoming loose.