shower mystery: suddenly cold water

During daylight savings time I have no shortage of hot water to my back shower. Once daylight savings time ends (and the weather gets colder), there is a sudden shortage of hot water and I must cut my showers short or freeze.
I have a single knob to vary how much hot water/cold water I get, and I have noticed once there is no more hot water, I can 'overtwist' the knob slightly and there seems to be more available hot water for a short time.
My hot water heater is insulated, as are all pipes leaving the hotwater heater so heat losses I am not considering. Is is possible at the end of daylight savings time the local water company uses a different water source which is much colder (~10F) than the original source during the other parts of the year? Is there some component which is possibly faulty? Is it possible a timer exists within my system of which I am not aware which could be affected by the time change?
Any thoughts are appreciated.
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Owen Wilson wrote:

Do you have a energy saving time of day control for that water heater?
--
Joseph Meehan

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thats my guess.. i bet if you waited an hour you would have plenty of hot water. having a colder source would make no difference otherwise. it would simply be heated 10 more degrees.
randy
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