This is the rear view of the control, clearly showing the high quality spark plug shaped porcelain probe holder, able to withstand high pressure 145psi and high temperature 150c
We started manufacturing these units in 1972. Of the hundreds of units built in all that time we have only had one failure that was not caused by customer error, or other external forces
Apart from the switching relay there are no moving parts, the resistance of the water is sensed by a cmos logic integrated circuit., that is isolated from the Ac mains by a double wound transformer
Mounting horizontally in the boiler flow via a 1 1/2" dart union is recommended to facilitate annually cleaning of the high quality stainless steel probe. Although this is not strictly necessary, it would need to be done as part of the annual insurance check
