I had the same problem with CLK. I found the problem to be the PC board connector that holds the wiring from the firemans switch was loose or dirty, and it worked again after I mechanically agitated it. Just follow the wiring from the external timer.
2/27/18 I found the root problem and it was the solder joints on the control board for that long connector associated with the Fireman's switch. The solder had cracked on some of the connector pins possibly due to cold solder joints, high vibration, thermal cycling, or a combination of all three. I used a soldering iron and some solder to reseat the affected pins and the heater has not failed since.
Answers & Comments
I had the same problem with CLK. I found the problem to be the PC board connector that holds the wiring from the firemans switch was loose or dirty, and it worked again after I mechanically agitated it. Just follow the wiring from the external timer.
2/27/18 I found the root problem and it was the solder joints on the control board for that long connector associated with the Fireman's switch. The solder had cracked on some of the connector pins possibly due to cold solder joints, high vibration, thermal cycling, or a combination of all three. I used a soldering iron and some solder to reseat the affected pins and the heater has not failed since.