"Petey" wrote in message
oups.com...
I was wondering if anyone knows what could be wrong. My water heater
seems to heat water only after someone tries to use hot water. For
example, the first person who takes a shower in the morning has luke
warm water, but the people who take showers about an 1 hour after have
really hot water. It seems like if someone does use the hot water for a
while then it shuts down and then once someone requests hot water, it
turns back on. I checked and it's not an energy saving technique. Does
anyone know what could wrong? It's been doing this for as long as I've
lived here (about a year).

I suspect your WH problem is caused by the hysteresis properties of the
temperature switch. I found the following info at wikipedia...

Hysteresis can be used to filter a signal so that the output reacts slowly
by taking recent history into account. For example, a thermostat controlling
a heater may turn the heater on when the temperature drops below A degrees,
but not turn it off until the temperature rises above B degrees. Thus the
on/off output of the thermostat to the heater when the temperature is
between A and B depends on the history of the temperature. This prevents
rapid switching on and off as the temperature drifts around the set point.