Hot Water Issue

About six months ago I noticed that when I turn on the cold water in any of the fixtures in my house, it runs hot for 30 seconds to a minute and then turns to cold. The hot water for the fixtures operates normally. While this makes for a warm toilet seat in the morning on chilly days, the hot water going down the drain while I wait for it to cool down is expensive. The house is 30 years old. I have replaced all of the faucets and I am fairly certain I don't have anything cross connected (I have checked numerous times.)

Here is my question. Could a shower mixing valve failure be the cause of the problem, letting hot mix with the cold water supply? I believe the shower fixtures are original.

Thanks for the help.

Regards,
Woodward

If its a single handle mixing valve, like a Moen, it can be the source of your troubles. Many of times I get a service call for this exact thing. After ensuring there is no blatant cross connection ( washing machine hose hooked up to a cold water bib to hot water bib and both bibs turned on) I changed out all the single handled cartridges in the building and problem solved.

Both of our showers do have single handle mixing valves, and I do believe they are Moen fixtures. I will replace the cartridges. Thanks for advice.

Regards,
Woodward