On Feb 14, 1:04 pm, "George" wrote:
On Feb 14, 12:08 pm, "Bob" wrote:

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
that much???

Bob

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??
Cool huh?
When your water heater cools it does the same thing...only it is
stronger than a plastic jug.

George

Ok, I can buy that. But with the faucets closed, where's the air
coming from, the pressure relief valve backflow? And where is the
water that is replaced by air going?