There are (at least) 2 possible reasons for a check valve on the inlet
of a hot water heater.
1 - Some municipalities require a check valve to prevent the flow of
water from the house back to main.
2 - A check valve is used when a recurculating system is used to
prevent long waits for hot water at fixtures far from the heater.
If you do use a check valve, you should also use an expansion tank in
between the valve and the water heater. If you don't, you run the risk
of having water leak from your pressure relief valve when the water
heats up and has no place to go due to the check valve.
That depends. A house that I owned up until 6 years ago was on top of a
hill. When the water supply failed (e.g. when there was a fire on my
circuit and the pumpers went whole hog) the water from the tank got sucked
back into the mains and the heating elements on my heater burned out ...
happened several times ... I was forced to install a check valve.
- I am tempted to say that is impossible. Even if a siphon could be
- established, if no taps are open the water in the heater couldn't get
I'd like to agree, but this thread seems to indicate that its possible:
Read the last response in the thread.
On Sat, 23 Dec 2006 17:18:58 -0500, "Charles Schuler"
That is strange. They require "backflow preventers" (2 check valves)
on every water service around here. You might be able to contaminate
your own water lines but your water will never get back to the street.
As the others have asked, why? Siphoning the water tank dry sounds pretty
unlikely if all taps are closed.
But anyhow, your water meter may already have one as I believe most newer
meters are required to have them (<5-10 years). If your heater has an
expansion tank hanging from the ceiling on the hot side, then you already
If it is required by code, it will be required at the house supply
inlet, usually where the service enters the house (unless it is part of
the meter). It won't specify that it is neededon the water heater.
Someone else pointed this out but I will add it again. If a check
valve is placed on the heater inlet, then an expansion tank should be
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