On Aug 29, 11:27 am, wrote:
Got a shower upstairs that works fine for about 5 minutes, then the
water gets really hot, then colder and so on. This is happening
without anyone in the house using anything. House was built in the
late 70's early 80's I guess with a newer water heater and copper
piping. Any ideas?

your faucet valves are shot. most likely just the washers on them.

hot water heats the cold valve, causes expansion of washer and
associated parts, more cold water. everything cools off, back to more
hot water, cycle repeats.

couple of bucks to replace the parts. maybe an hour of labor.