If you leave water inside plastic timer or plastic hose parts, and water freezes during winter, then the plastic will split as frozen water expands.
Buy new water control.
Open link below for some Gardena manuals including T1030
http://waterheatertimer.org/How-to-program-Gardena-C1060.htmlBy the way, if they made the same parts out of brass or copper, the brass and copper would expand instead of crack during a freeze, but the internal valves would be ruined anyway.
So plastic is a good material, just bring these things indoors or drain the water for winter storage.
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