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).
It would help if you gave us more details like, is it a gas fired or
electric water heater?
In any event, I've seen this in a vacant cottage that I have.
The water remains lukewarm from this gas water heater. After there's
been some draw down, the heater brings the water up to full temp.
What I think is happening in my case is that the main gas valve is
sticking. This is the valve with the thermostatic temp control.
I had the gas shut down to it over the summer and after being relit,
the problem was even worse. I suspect that the valve gets gummy with
age and or sediment buildup from sediment and moisture in the gas
The solution? Replace the gas valve. However since the price of just a
new gas valve is about half the price of a new water heater, I suspect
that the best bet is to replace the heater, especially if its got some
age on it. In the meantime, try simply turning up the temp on the
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.
It's a gas water heater and the house and water heater are only 4 years
old. I don't have the make and model of the water heater on me right
now, but I can get it. I've already tried turning up the temp on the
valve, but that doesn't seem to make any difference.
Is there a way to find out if my temperature switch has hysteresis
properties? I looked at the water heater manual and I didn't notice
anything about this.
The hysteresis is built into the gas control
to avoid frequent cycling of the burner.
They are something less than a "precision" device
though and c hanges like you are seeing do occur over time.
The control is not "repairable". You can, however,
replace the gas control. Or, at least someone can.
A heater which is 4 years old may be worth investing
a new control in, considering what heaters cost today.
You do the legwork to find out what it would cost
for a new control where you live.
I think you are just screwed. My gas water
heater does the same thing, but it is due to the
great difference between turn on and turn off
temperatures. I don't know about the hysteresis
stuff, but if you look at an attic thermostat you
will find that it has a 10-15 degree differential
between turn on and turn off. My gas WH has at
least a 10 degree and maybe more differential.
Previous info on this group indicated that it is
quite common with gas heaters. My previous
electric water heaters only had a 2-3 degree
differential. I still have the thermostats out of
an earlier one (finally eroded a hole an leaked)
which I tested thoroughly in preparation for use
in a different application. There is no guarantee
that a new one won't have a large differential also.
As other posters are mentioned, your situation is normal and intended. You
just have to find a compromise setting where the water is a little too hot
sometimes and not quite hot enough at others. This characteristic is
intended to reduce cycling of the burner and thus conserve energy.
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