Sigma EF430st [pa] and k10d will it work??

I have just bought a s/h Sigma EF-430ST [PA] flash to use with My K10d.
Has any one used this combination and got it to work? It is with the PA designation for Pentax but I can't get it to work, or more correctly get it to work correctly.
it does not always trigger and has numbers that illuminate across the back 28-35-50-70-90 this occasionally changes from the 28 to the 50 but I have no idea why or what it is tying to do/show?
Help any one please , I'm sure the flash is OK it's just a setting thing, no manual and can't find one on line.
Alistair

Gareth, thanks for the reply, what you say is what I assume as well but it dont work correctly, Oh back to the shop tomorrow, thought it was to good to be true.
Alistair

I had used one of these for a while with a MZ6. The results were not great and the zoom head was erratic and not adjusted correctly with some of my pentax lenses. If I recall correctly it is a TTL gun and therfore will only work in manual mode on the K10. Not sure of the trigger voltage.