I should also add that this switch is located in a room adjoining the boiler. There is also a large hot water tank in the room. Their old boiler would occasionally emit soot into this room. The switch is dirty with the stuff, not a heavy coating but definately dirty. I know that the oily soot can be conductive. I told the customer that I wouldn't want to replace cards until they took care of the problems. The old boiler finally broke down this winter and they replaced it with a much more efficient one. They've also vented the room and added a fan to circulate the air to help cool the room down. I put a thermometer in there with a memory that would let me know how hot it gets in there (and to show them). It has reached highs (pre vented days) of just under 110 deg F. Their venting has cooled it down a bit, hoever, it still can reach temps of 100. I believe 105 is the top end for operating temp?