Q: Changed brake pads and no obvious fluid leaks, brake pedal goes to floor with no resistance.

When you replace your brake pads you had to push back the caliper pistons to get the pads out and the new ones in. After the calipers are put back on you will have to pump the brake pedal several times to pump it up using short strokes.

If you pushed the pedal to the floor then you may have to pull the pedal back and then use short strokes until you get a hard pedal. This is normal. Now after you try pumping the brakes up and the pedal keeps going to the floor, then you either have a leak somewhere or the master cylinder has excessive debris inside it and caused the pistons to get damaged. You would need to replace the master cylinder. If you want to have this looked at in person before doing a repair, a certified technician from YourMechanic can come to your home or office to verify the cause of your braking issue first.