I live in a condo where the hot water is supplied by a boiler system. Typically it takes a minute or two for the hot water in my unit to get hot but I have one bathroom sink that provides immediate hot (really hot) water, and where the supply hose and valve are hot to the touch even when the water is off. None of my other faucets do that and this one is in the middle of my unit (not any closer to the boiler than any other faucet).

The 2nd bathroom sink in the same vanity also has an issue of a smell when the hot water is turned on. It actually seems to be more of a smell from the drainpipe rather than the water or faucet but I've cleaned the drain several times and it gets better but then comes back. Now I'm wondering if it's related or a separate issue.

I'm afraid both of these things are pointing to having to open up the wall and see if there's a leak happening. We had a major flooding incident from an attached unit 2 years ago which required new flooring and drywall in 4 rooms in our unit (the plumbing is from the early 80's and there are leaking issues throughout our complex). I am dreading another round of having my house torn up. Do I need to just bite the bullet and open up the wall to see if there's something leaking? Is there any way to identify what's going on without cutting holes in the wall and/or taking out the vanity? Thanks for any advice you can give.

google 'borescope'

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"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638

Typically in a multi resident building a hot water recirculating line is installed it’s possible the recirc line is tied to that bathrooms lavatory sink hot line… so instant hot water

As for the stench it could be bacterial growth in the trap or pop up piping try dumping bleach down the drain to kill the bacteria

Does the sink have an overflow passage? If yes, that also needs to get cleaned.