Quote:
Originally Posted by Flybob
It is possible that it was coming from the WH in a reverse flow. There is no back flow valve on most water heaters. What faucets did you have open. It is always a good idea to drain the WH prior to opening the ow point drains so that any debris in the WH is not sucked into the cold water line and left in there to clog toilet, faucet or shower valves when you use the system again.
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X3. On water heaters without backflow preventers/valves.... When you remove the pressure on the lines, then there is nothing to keep the cold water pushing into the hot water heater, and thus pushing the hot water out into the hot water line.
The water in the heater tank will then backflow back into the cold water line via gravity, and thus out your cold water low point drain.
This schematic may help you visualize it better: