Ok, I have a cabin in the country. Because the propane WH is getting
close to being old, when I'm not going to be there for a week or so I
turn the water inlet valve off and the thermostat to pilot. That way
if it leaks, the water spilled will be limited to 40 gallons.
Anyway, when I turn the water valve back on after a week or two, there
is a good amount of air in the tank and hot water lines. There is no
water around the heater. There is no indication of rust on the tank
burner or tank bottom. I crawled under the cabin and there is no
water spotting on the subfloor, nor water on the vapor barrior.
So I'm puzzled. Where is this air in the tank coming from? I'm
talking about air/water spewing for up to a minute. First thought was
a leak and second thought was volume contraction due to cooling. But
Cooling water heaters suck
It's probably "sucking air" when it's off.
For a demonstration try this fun experiment, get an empty gallon
plastic milk jug and put a 1/4 cup of water in it, now stick it in
the microwave (with the lid OFF) just long enough to get the water
good and hot, now take it out and screw the lid on and let it cool off
(you can set it in the fridge if you want fast results)....see what
happens to the jug??
When your water heater cools it does the same thing...only it is
stronger than a plastic jug.
I would guess either the PR valve or the air could be coming from the
water. Water does absorb air. How much air depends on the temperature and
pressure. Have you not noticed that sometimes when you fill a glass with
water (during the winter) it is milky looking. That is air that was in the
water. The time of year and the change in temperature of the water may be
forcing dissolved gasses.
A good possibility. First water flow is somewhat opaque, then clears.
I never thought to relate it to air in the water. Would also explain
why the total volume in the tank wouldn't change. Sounds like the
best explaination yet - even better since it doesn't relate to a
problem. (I don't think).
But how can it suck air into a tank that is full of water without
forcing some of that water out somewhere? Wouldn't there have to be
much less pressure inside the tank than outside? Since liquids cannot
be compressed, there would have to be air already in the tank for a
Does it either way. With the main on first, you can hear water
entering the tank so the air is in the tank prior to any valve being
opened. The more I think about it & discuss it, I'm leaning to air in
the water as it enters the tank, then separating as it sits. Water
comes from a saturated sand aquafir so I can understand how water
movement down there could induce air into the mix.
Do you have an anti siphoning device on your water heater? This can
occur without one, either naturally or when work is done on the lines.
Around our area it's a standard item to have.
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