Brad Ford wrote:
I've got a cool little Wrench Force floor pump that will accept
Schrader or Presta. I've used it for over a year exclusively to
inflate my Presta road tubes. Got the kids bikes for Christmas, pumped
them up (Schrader valves), and now (several weeks later) the pump won't
blow air out the Presta hole any more. It's supposed to be "auto
sensing". Is it just buggered? What would you all try to debug this
problem?

I've had the same problem with my Wrench Force pump. Quite annoying!

It's especially bad when trying to inflate from 0, e.g. a completely
empty inner tube. It seems to me that the pump sometimes "corrects
itself" if I install it on a partially inflated tube.

Otherwise I get frustrated and bang the pump head on something hard
until it behaves.

If it keeps it up I'd ask for a new head from the dealer. They're easy
to remove and replace without tools.

Good luck!