Hello thanks in advance for your help. It'* probably a dumb question to ask but I will do anyways.
i changed the brakes and after I was done I pumped the peda with car off and everything tightened up good. Once I started the car I could hear air escaping from, it sounded like near the brake pedal, but nonetheless it goes to the floor when I brake. Like I said with car off it tightens up extremely stiff if I press pedal. My question is do u think it could be a bad check valve or is it the actual booster or am I way off and is it the master cylinder, I don't see any fluid leaking inside car or anywhere.

Year, make, model, ABS?

What exactly was done?

Did you open up the system, to bleed, or was there a leak?

1998 Buick Regal ls
mall I did was literally change front brakes and once I was done changing both of them I went into driver seat to pump the pedal and while I was pumping them got tighter but I also heard or felt like a air rush come out sumwhrre, after I pumped the brakes I started the car to drive it and when car was started and I checked the brakes once again the pedal went to the floor, I shut off car and pumped the brakes again they seemed to get extra tight like almost to the point where was no play at all while engine off. I started it again and checked brakes and pedal went to floor and I could hear air escaping the pedal when I pushed them??

When the pedal drops to the floor, do the brakes still work?

Actually I couldn't tell u for sure becusee the pedal literally locked up to where I couldn't even push the brakes anymore it wouldn't budge.