Why does a cold water tap run hot before it runs cold? Why could this be a problem? Steve

Steve, this is not normal at all. Do you have a water heater or a combi boiler?

Steve,

Do you have a water heater recirculating pump installed on your heater?

John

Hello steve, what region do you live in? And do you have water piping overhead in the attic? Out in the southwest the water piping can get very hot in the attic during the summer if the lines are not insulated.

Afaroo has the best question...

Also, there is a possibility that your pipes touch and heat from hot water pipe transfers onto cold water pipe while water is not in use.

Moreover, these days in So.California we get luke warm water from our cold water side as cold water is being run in the attic. Attic gets quite hot warming the water in cold water pipe.

Another take on this could be when the hot water expands in the water heater it expands out the cold water inlet a ways into the cold water side.
When a cold water draw is made the expanded hot water gets sucked up into the draw and will run hot until the cold water replaces it. A check valve on the cold water inlet to the heater will prevent this from happening. Just another explanation. Tom