Well, all i had to do was to disconnect pressure switch wires and connect flow switch wires instead. Flow switch had white and brown wire. Didn't matter which one where - worked both ways.
Unfortunately, replacing pressure switch with flow switch didn't solve my problem. When you have a leaky oring or downstreamer leaks a little back into the bucket, or your gun is worn out and seeps some water through - your unloader keeps cycling to try to build back the pressure in the line. Every time it cycles - burner kicks on for a second. I had hoped that if I use flow switch burner will not be kicking in when machine is in bypass and oring in the high pressure line is dripping. No luck, with flow switch if my PA VB10 unloader cycles in bypass and out - burner still kicks in. I guess there is more than 1 gpm of flow during that unloader cycle.