Hello and thanks to this forum and others

I have a recently acquired S26 which has been descaled and a new screen and pump fitted.

I'm temporarily running it off a syphoned water supply but I'm struggling with my shots as the machine is choking on anything larger than a single shot of average grind and tamp. I've experimented with grind and tamp without any improvement so without being able to measure the pressure at the group head I've come to the conclusion (correctly or incorrectly) that the pump pressure is low.

The 3 way valve doesn't look adjustable, is my only option to alter pressure adjustment at the rotary pump? Any advice gratefully received.

PS...to increase pressure at pump adjustment screw, anti or clockwise?

See Adjusting espresso machine's rotary pump brew pressure? and similar threads for instructions. Briefly, the adjustment screw on the rotary pump controls a bypass valve that allows water to pass directly from the output side to input side. Counterclockwise = less tension on bypass valve spring = more water passes directly from output side to input side = pressure falls. See "pressure adjusting screw" in the diagram below.


Small turn of pressure adjusting screw! Use one-quarter turn increments, then test pressure

In a rotary pump espresso machine, the over-pressure valve is typically set to 12 bar to protect the hydraulics system from excessive pressure during warmup (unlike vibratory pump setups where it does double duty as expansion valve and maximum brew pressure adjustment).