NASA and rocket-builder United Launch Alliance plan to make another attempt to get the long-awaited mission off the ground Sunday at 3:31 a.m. EDT (GMT-4), the opening of a 65-minute window, assuming the problem is corrected by then.
The launch now is planned for Sunday, August 12, from Space Launch Complex-37 at Cape Canaveral Air Force Station.
The reason for the delay was not immediately clear, but was called for after a gaseous helium alarm was sounded in the last moments before liftoff, officials said.
"Eight long years of hard work by countless engineers and scientists is finally paying off", Adam Szabo, the mission scientist for Parker Solar Probe at NASA's Goddard Space Flight Center in Greenbelt, Maryland, said in a statement.
The probe's main goal is to unveil the secrets of the corona, the unusual atmosphere around Sun.
But these solar outbursts are poorly understood.
The heavily shielded Parker Solar Probe will make 24 such close flybys over the next seven years, getting within just 3.83 million miles (6.16 million kilometers) of the sun's surface at closest approach.
The probe is protected by an ultra-powerful heat shield that is 4.5 inches (11.43 centimeters) thick.
The heat shield is built to withstand radiation equivalent up to about 500 times the Sun's radiation here on Earth.
Even in a region where temperatures can reach more than a million degrees Fahrenheit, the sunlight is expected to heat the shield to just around 2,500 degrees Fahrenheit (1,371 degrees Celsius).
Sending a spacecraft closer to the sun than ever before, it will embark on a almost seven-year venture, becoming the first spacecraft to have a direct encounter with a star.
The mission is named after famed solar scientist Eugene Parker, and is NASA's first to be named after a living person.
The probe will fly through the sun's corona to gather data on the sun's great mysteries, such as the solar winds that create aurorae on Earth and disrupt satellites and power grids.
The probe will be controlled from the Mission Operations Centre based at the Johns Hopkins University Applied Physics Laboratory (JHU APL), which is where NASA handles its unmanned missions.