vaillant eco tec pro 28 diverter valve leakage?

I just have a deep look in the vaillant eco tec pro 28 after having problem with this that presure is keeps going down! when i have a look in the boiler there was loads of water leaked, after soaked it out all i tried to find out where it leaks from, so finaly find out that it leaks from diverter valve when we open hot water taps only. Is this possible to fix it as it is or its time to replace it with the new one? and can i change it myself or need an experts help? many thanks.