My cold water at the sinks runs very warm before it turns cool

Is this a new house and if not do you have a circulating hot water system in your house.

Follow your cold supply pipes back toward the incoming supply from the street. Do the pipes ever come in contact with an air duct or the water heater? Do you have an expansion tank on the water heater, it could back up a small amount of heated water if everything isn't working just right.

If you have a recirculating system installed, and the sensors fails you will have hot water in the cold line in the beginning, please come let us know if you have the system installed and we will till you how to check and replace the sensors, Thanks.

John

Follow your cold supply pipes back toward the incoming supply from the street. Do the pipes ever come in contact with an air duct or the water heater?? Do you have an expansion tank on the water heater, it could back up a small amount of heated water if everything isn't working just right.

Uninsulated cold water piping run through floor joists/stud bays with a hydronic heating system could also be a factor.

With hydronic systems being so popular these days, we've taken to insulating all of our water piping to prevent heat transference.

my cold water at the sinks runs very warm before it turns cool
Do you have a recirculating system installed? If not then this is called "convection". The heat works its way out 0of the heater and up the cold water supply. When you make a draew some of that hot water gets sucked up into it. The solution would be to install heat trap nipples, (See image) in the water heater inlets. Good luck, tom

Also, this happens when uninsulated cold water line runs through attic.