Hot water is crossing over into cold water. Do not have a check valve on water heater. Also, do not have any single spigot faucets. How do I test to see if it is happening in/through 1 of my faucets?

Hot water is crossing over into cold water.
Do you mean the hot water pipe cross over the cold water pipes?
So what?


Do not have a check valve on water heater.
Water heater do not normally have check valves.


How do I test to see if it is happening in/through 1 of my faucets?

How do you test to see if what is happening?

Close cold water valve located above hot water heater / above cold water inlet. Go to your sink, turn hot water ON for 2 minutes. See if you get continuous water flow after 2 minutes out of the Hot Water side.

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Milo