It sounds to me like the diverter valve still isn't working properly. I'm not sure what you mean by the fontpin, but if you mean the pin that moves out when the diverter valve operates for hot water demand, then this is most likely the problem.
If you have already changed the diaphram, dismantle the valve again and clean any deposits from stuffing box through which the spindle passes and make sure it can move freely. There is also something called the venturi which generates the pressure drop which causes the diaphram to move. Make sure this isn't blocked.
I'm not sure what the second diaphram you refer to is.
Mark
December 2010
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