Im in Houston and my water is 56 right now. If the SWG temp sensor wasnt messed up it would have stopped producing by now. I use the dummy cell as well. I just disconnect the cell and hold the power button on the control box and it doesnt come on anymore. Perhaps try powering off the box before disconnecting the cell, so the cell connection error wont hang you up?
I have it wired to my single speed timer as well. If the power button wont work I suppose you can disconnect it from the timer just be careful. If you have the usual Intermatic timer, a few of those screws are always hot with 220v so turn it off at the breaker. I also put dielectric grease in the cell connector on the box and tape over it. The first winter I used the dummy cell, there were dead bugs in there for some reason.