Hot water OFF in Y plan

[ant101]

Hi,
What is the purpose of the 'hot water OFF' terminal in a programmer on a Y plan. I notice it goes from cyl stat 2 through the grey wire to the 3 port mid pos valve. What is its function.

I have also read that when heating and HW are both off the valve motor is de-energised and the valve is open to the HW circuit. I have noticed that the valve has stayed in the CH open position if turned off in that position.
Hope im making sense,
Thank you,
Student

 

[shambolic]

It sends power to the boiler and pump on side of the end switch. As the switch would not be made as valve not in open position