I had a strange fault presented to me today. The house R.C.D. had tripped off. The cause was a leaking central heating pump that had let some water drip onto a 2 port valve. The water had gone inside the enclosure of the valve. The micro switch was located at the bottom of the metal enclosure. One of the micro-switche's terminals had a maker's plastic tape over it, factory installed to prevent the terminal touching the inside of the enclosure. A high point of the soldered terminal wire was in close contact with the plastic insulation and seemed to have caused a hole to appear in the plastic insulation tape thus creating a L. to E. short circuit. I can not be sure if the water was a contributing factor in the short.

After drying the micro-switch with a hair drier, and moving the metal cased wall away from the micro-switche's terminal, the valve was put back into service until it can be replaced with a new one.

I think that lack of use of the central heating system had allowed the water to accumulate, but under normal circumstances the hot pipes would have caused the water to safely evaporate. The house had been recently sold and had be unoccupied for some time.

Z.