Problem with honeywell st6400c??

[gardencityserv]

I have recently been to an address and the problem is that when hotwater is calling it fires boiler, but switch off hw and select ch the boiler goes to fire then clicks out..... but when both hw and ch is selected boiler fires and i get heating and hotwater......maybe 3 port but im edging towards programmer... any ideas??

 

[tamz]

It is the 3 port. Sticking / fkd microswitch (the one with the orange wire).
If you don't know how to fix this, change the valve.

 

[gardencityserv]

thanks for your help, will try this