Halstead Ace High Diverter

[MANDATE]

Just trying to get a better understanding of the operation of the Ace High Diverter Valve.
On the DHW side I understand that opening the hot tap (mains water)releases the pressure on one side the diaphram, causing the diverter to move. This opens the path to the 'heat exchanger' and closes the path to the 'heating circuit.
It also activates the DHW micro switch to light boiler.
When tap is turned off, it must return to original position.

On the CH side the diverter is already in the correct position and the CH micro switch is activated by a vertical pin. Beneath this pin is another smaller diaphram.
The question is 'How is the pressure under this diaphram increased when heating switched on? and decreased when switched off.

Anybody like to explain it

 

[transam]

pump pressure , this is a primary circuit flow switch , & will activate whether the boiler is in H.W or C.H mode , unless this switch/dia' operates the boiler will not fire .

 

[MANDATE]

Thanks transam! I thought there was no relationship between the two micro switches.
Now I take it as follows:
Heating: (a)Switch on and 'pump' runs
(b) 'flow' switch operates and boiler lights

DHW: (a) Hot tap opens, diverter moves across
(b) 'DHW micro switch switches on and pump runs
(c) 'flow' switch operates and boiler lights