I live in an old house (1956), house has a gas hot water heater, (18yr old) only one bathroom so no one feeds off of my hot water heater except me. When I take a shower, the temp. of the water will fluctuate. The bathtub has a three handle water supply fixture and it is about 5 years old. Even when I draw the water to take a bath, the water temp. fluctuates, so that kind of rules out the mixing valve on the faucets. Does anyone have any suggestions on this problem?