Hi There.
We just bought a house and noticed warm water coming out from a cold side faucets (especially up stair bath very hot) through out the whole house that including all faucets , toilet and two out side faucets too ( every time we water the plant the water heater kick on) we have two water heater one is in the garage and other one is upstair. Is some one know what cause this problems.please help thank you.

Check the way your hot water is set up, for example I have a combination tap in my laundry that if left open on hot, say a feed into a washing machine, the hot water will flow into the cold water pipes and I can get hot water in an outside tap, this also allows cold water to feed into the hot taps in the shower. It is possible you have an open connection on the hot water side, perhaps in a water mixer.