[beforudo]

Cold water is getting into the hot water piping system.if I disconnect the hot water output pipe and turn off the valve to the cold water inlet to water heater cold water water shoots out of the hot water pipe outlet pipe with full water pressure.

[massplumber2008]

Sounds like a cross connection, for sure!

Try turning the shutoff(s) to your washing machine off and see if the cold water stops flowing into the water heater... if so, the washing machine solenoid valve needs to be replaced.

If that fails to show the problem, continue looking for any connections between hot and cold... like an outside faucet with hot and cold piped to it.

Otherwise, you can try shutting off a single shutoff to every single handled faucet in the home and open them up one at a time until you find the defective faucet.

Finally, you could have a problem isolating single handle shower valves... in this case, do all the above and if no issue is found, then most likely, the shower valve mixing cartridge is defective and probably needs to be replaced.

Mark

[beforudo]

Your right it was a valve to a single shower with out any faucets... found that valve and turned it all the way opposite of where it was set and it decreased the water pressure coming from the hot water faucets when I turned off the hot water inlet valve... thanks for your response... I can have peace of mind now... THIS HAS BEEN BUGGING ME SINCE SUNDAY.

[massplumber2008]

Glad you are all set. I would recommend replacing the mixing cartridge at your earliest convenience.

Thank you for updating the thread!