Two identical tube failures
 

Hello all. I'll try to keep this short and quick, any insight would be great. About two weeks ago I bought a Trek Valencia. Fantastic bike, but I've had one tube failure on the front wheel and one on the rear wheel. In both cases the rip/tear on each tube occurred right at the base of the valve. It's running the stock Bontrager HardCase tires (700x32c, presta valve). Also I am 6'1, 250lbs if my body dimensions are a factor. I replaced the front tire tube a week ago, and the rear one about 10 minutes ago with a Bontrager tube. I'm not sure whether the stock tubes were junk, or if it has something to do with the fact that when I bought and rode the bike home(20kms in city), I discovered that the shop had the tires at 20psi/60psi (front/rear respectively) instead of the maximum 110psi. Both flats occurred while removing my floor pump head from the valve of the tire.

pull the pump head straight off. riding with low psi can cause the tire to slip on the rim and move the tube with it. that may have misaligned the valve and you pumping it up finished the tube off

Thanks! I figured that was the most plausible explination.