Jim,

Rather than debate the three port valve theory, and allow them to mess with your finances a bit before they finally get around to it, why not get them to replace it, no questions asked.

The worst that will happen is I've been wrong, I made you spend $56 for the valve and 1/2 hour to change it. It's coming up on 9 years of age anyway so its life is nearly over. If that was not it at least you haven't paid for more soapy solution and that can be ruled out.

BTW, if Hector has agreed with my analysis I feel very confident in it because he is unmatched in analyzing these systems and taking the complexity out of understanding them.