Valve leak at pressure test

I'm doing the final connections on a tub. I have sweated together hot and cold water valves to the filler stem, although water lines are not yet connected. To check progress I closed the valves and literally put my mouth over the stem and did a rudimentary air pressure check.

I heard a hissing of passing air, and it appears the leak is out of the bottom of the hot water valve. When I use my hand to block the fitting where supply will connect, the system is at least tight to what ever air pressure I can supply. This is a brand new Kohler K-300 system, so I'm surprised.

Any ideas? Is this just a tightening of a nut on top of the valve? Could I have damaged anything inside while sweating connections?

Help is greatly appreciated.

Jon

Its hard to say.
If it's one of the Kohler valves that uses rubber seat cups similar to Delta there may not heve been enough pressur to set the seat.
I'd turn on the water and see what happens.

ceramic disc valves

Thanks Redwood. Literature I find says it uses "ceramic disc valves" - is this in lieu of any rubber rings / seat cups?

Try the water test