Pilz PSS SB FT, Basic license - Manual (Page 115)

Modular Block System: Burner Management 6-71
Loss of maximum pressure signal as valve VAV3 or VAV4 is incorrectly seated
The RDY bit and the ENBL output are reset if the max-pressure monitor
responds during the seal/pressure check.
ENBL is simply set to “0” for one program cycle, as SyOK is simulated to
remain at a constant of “1” and as such is acknowledged immediately.
In the complete program this is not possible because of the sequential
operation of the individual blocks.