Sorry - I got the clockwise and anti-clockwise the wrong way round.
It meets an end stop when I turn it anti-clockwise. Is this setting "1"?
The numbers increase when you turn it clockwise
I recently had a Honeywell DU145 bypass valve fitted, with the factory setting of 2
Using data from my boiler and my pump, I calculated that it needs to be set at 3.5. I loosened the locking screw as per instructions and was surprised that the black dial moves with the red control - not very...