It was next to the hot water line and not insulated (enough) and it had pretty much just been sitting there all night.

Lucky you didn't get legionella. That is not up to spec, cold water lines should always be below 25°c. I have never seen such an installation, even in development countries it was done correctly.

> That is not up to spec, cold water lines should always be below 25

Yikes, that's tough. In my city, the cold water pipes are buried close enough to the surface and the brutal sun that it comes out of the tap about 27-29c during the day.

same, been in two developing countries with similar heating system, never seen such a problem. sounds disturbing

It's possible there's a faulty faucet mixing valve somewhere in the building causing hot water to mix into the cold line.

The hot water from the cold tap reliably went away once the water started running which is what made me think that it was sitting still next to the hot water that caused it