JKid makes a good point, re-test to confirm it was not the tester.

 

Agreed. I actually got the tester kit from O'Reilly's yesterday after a week of waterfall noises coming from the dashboard. Odd since all the cooling system was new. Turns out it was a hose clamp that wasn't tightened by me all the way. New hoses need to be checked since the clamps still need to finder their "seat".

 

Also, I wouldn't go higher than 20psi. 17 is plenty enough to find leaks. Ideally, do this test when the driveway is dry and clean, or put butcher paper under the car so the leak drip will be evident. Things to look for, weeping out of the water pump, loose hose clamps, and in rare cases, that water pipe under the intake manifold. You can see it with a good flashlight. Also check for weeping around the throttle body heater. Oh, and I guess it's possible there could be leakage occurring inside in the heater core, but doubtful if you haven't noticed wetness inside.