I'm having a bizarre problem. At least it's bizarre to me.
I'm repacking a HW faucet connected to our washing machine. To do so, I turned off the HW heater, and then the valve on top of the HW heater.
I then opened up the HW faucet on the sink in our downstairs and upstairs bathrooms to drain as much water as I can out of the loop. Works fine. No hot water coming out of any faucet now--including the one for the washer.
Then my son enters the bathroom and turns on the cold water. It sputters for a second but then comes on as you'd expect.
Now here's the weird part...suddenly, water comes sputtering out of the HW faucet for the washer!
Turn of the bathroom cold water, and water stops coming out of the HW faucet for the washer. Turn it back on for 10 seconds, and we get 10 seconds of water coming out of the washing machine faucet.
Now it's an experiment. We discover that any bathroom will cause this (As they are stacked, so likely all on the same wet wall). The kitchen faucet will not cause it.
What's going on here? Is there some natural siphoning thing going on somewhere in my system where cold water is being siphoned into the HW line? Or do I just have very messed up plumbing?