I have a leak from the dhw manifold where it couples into the 3 way valve only when I turn on the hot water tap. I have replaced the o ring & seal at the centre of the manifold but only suceeded in having no hot water or leak!!! EVENTUALLY, When the pressure builds up, the pin at the centre of the manifold activates the plunger to activate the micro switch. HOT WATER & LEAK return!!! I replaced the Domestic hot water manifold for a new one & this cured the pressure problem but I still have the leak. It would appear that there is no seal between the manifold coupling & valve only a flat surface between the two devices & the manifold is held in place by two grub screws. Should I seal this joint or is the leak backwards from the valve as I cannot imagine the new manifold is faulty.