Honeywell SDC - Manual (Page 48)

Operation SDC / DHC
48 EN2H-0220GE51 R0308
ATTENTION
With the setting value ALL, all heating circuits and the hot-
water circuit are overwritten with their default switching
times with regard to the selected program.
When overwriting occurs, individually created switching time
programs are permanently lost and must be recreated from
scratch.
Pressing the button causes an immediate return to the basic
display.