Water Heater
Because electricity is more expensive than gas, electric water heaters are far
less common. It costs about twice as much to heat water with electricity as it
does with gas, and electric water heaters heat water about half as fast as a gas
heater.
Water Heater – How It Operates in complete detail (electric)
Understanding in detail how your water heater
works will help you to trouble shoot it should anything go wrong.
A water heater can exhibit some strange behavior
At first glance your water heater seems pretty simple. But there are things that
can go wrong with your heater that are quite unexpected.
A water heater is a cylindrical tank, enclosed in insulation, and covered with a
sheet metal outer covering. Normally there will be a conduit connection on the
top of the heater for hard wiring an electrical connection to the heater.
The water temperature is controlled by a thermostat
Most electric water heaters have an upper and a lower thermostat. Typically the
top and bottom electric heating elements connected so that only one heating
element heats up at a time. Normally the it's the upper thermostat that
activates first, and when the top is hot, the upper thermostat connects the
electricity to the lower thermostat. If the lower thermostat is below the set
point, then the lower heating element turns on.
High limit switch
If for any reason the water in the tank becomes too hot, it will trip the high
limit switch, (a circuit breaker). The high limit switch is mounted with the
upper thermostat, and has a red reset button. If the high limit switch trips, it
must be reset by pushing in the red button.
The dip tube is critically important
Water flowing into the inlet is directed through a long thin plastic tube to the
bottom of the water heater. If the dip tube is missing or broken off, the
incoming water doesn't flow to the bottom, and just flows across to the outlet.
This makes it seem as though the water heater is not heating the water very
well, or it can seem as though you run out very quickly.
Since the dip tube directs the water down to where the thermostat is located,
running even just a gallon out of a faucet can cause the thermostat, to turn on
the gas valve. The pilot light ignites the gas and the water heater begins the
heating cycle.
Hot water stacking
The heated water in a water heater can form layers with differing temperatures.
When frequent short uses occur the water heater turns on and off and causes the
water at the top of the heater to get hotter and hotter. It’s called “stacking”.
It’s because hot water, like hot air, rises. The water can get hot enough to
cause the TPR safety valve to open and release hot water from the heater, even
if the thermostat is set on low.
The TPR valve is a safety device (TP valve, T/P valve, T&P valve)
The TPR valve is a safety device that opens to relieve pressure if the pressure
or the temperature gets too high. This will prevent the heater from blowing up
if something goes wrong. The TP valve usually is typically located on the side
of the tank near the top.
When your water heater heats the water, the water expands and as the water
expands some of it gets shoved back into the cold water line, and into the water
main. If there is a check valve or some other obstruction between the heater and
the water main, then there is nowhere for it to go, and the pressure begins
building up.
Thermal expansion tank
If for some reason the TP valve does not open to relieve the pressure the water
heater becomes a bomb and can explode with amazing power. But you don't want
your TP valve openning all the time, so to solve this water expansion with
pressure buildup problem you can install an expansion tank at the inlet.
An expansion tank is a pressurized tank with a rubber bladder or diaphragm in
the middle. As the water expands, it moves into the expansion tank compressing
the air in the bladder or on the other side of the diaphragm and that way
excessive pressure does not build up in the water heater.
Usually local codes require the outlet of the T&P valve to be plumbed down to
the floor, or outside to the ground.
What is sediment and where does it come from?
When water is heated, the dissolved minerals in
the water can precipitate out and settle to the bottom. The precipitate is
called sediment. If you live in an area with hard water, over time your sediment
can build up to pretty significant levels. If the buildup is large, the amount
of water held by the water heater is reduced, so you could run out of water more
quickly.
The anode protects against corrosion
Water heater tanks are internally coated with
epoxy or have a glass lining. This is to prevent rusting and corrosion. To
further fight corrosion water heaters have a magnesium or aluminum rod called an
anode inserted into them from the top. The idea is that the anode will corrode
instead of the tank.
Smelly hot water -- rotten egg odor
Anaerobic bacteria can get into the tank and
react with the magnesium or aluminum in the anode to form hydrogen sulfide
gas which smells like rotten eggs. This is more common with well water than from
city water mains.
Sometimes replacing a magnesium rod, the more
common one, with aluminum can help. There are also some special (and expensive)
anodes that are supposed to solve the problem. Anther method that works is to
sterilize the tank and the hot water pipes with bleach or hydrogen peroxide.
However, the bacteria can come back, especially if you go away for a time and
the water just sits in the heater for days or weeks. Other than the awful smell
the bacteria will not harm humans.
Drain valve - replace it with a ball valve
At the bottom of the tank there is a drain valve. If you live in an area with
hard water and you have a sediment problem, then you should probably replace the
plastic drain valve that most water heaters come with now days with a full flow
ball valve. This will make the tank much easier to drain and flush.
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