DCI’s most recent experiments with a wide range of the LHP configurations (from kilowatt systems with parallel condensers for deployable radiators to miniature few-watts-LHPs for cooling electronics) have discovered a new, interesting phenomenon that we called the “cold shock.” Initially, the cold shock behavior was discovered during routine acceptance tests of large LHPs with large-volume condensers. Traditional power-up steps appeared to lead to unexplainable temperature instabilities and significant temperature overshoots when the condenser was initially very cold. After the occurrence of these anomalies we performed hundreds of experiments on dozens of typical LHPs, trying to understand the overshoots and find ways to avoid them.