If you forgot to shut the bypass valve and the toilet is the closest cold tap to the water heater, then you will get hot water to it. Especially if all of the faucets have been off for some time. Higher pressure in the heater and a check valve will have the hot water flowing toward the nearest open water tap until pressure drops and opens the check valve. Double check your de-winterize process.
Heat transfer between hot and cold lines is not likely to be significant unless hot water is continuously flowing thru the hot line. Same thing with an issue with the outside shower, since the lines are not insulated, hot water inside the line cools down very quickly if the water is not flowing.
Texas Baptist Men-Retiree Builders member since '01
13 Silverado 3500HD D/A, 2wd CCSB srw, custom RKI bed
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