Right… but if there’s a furnace in your unit that isn’t properly vented that’s your priority.

Only if it’s gas. It’s a combustion byproduct.

Okay, then yeah, it’s pretty typical to just shut off the cold water feed to the water heater. Pull the cord/flip the breaker, whatever it takes to turn it off… open all the taps if there’s water pipes above it so everything drains, then replace the faulty valve in the tub.

Same concerns though, if the furnace isn’t properly vented you’re going to be breathing carbon monoxide. That absolutely must be corrected, the unit is not safe to occupy and any municipality will red-tag the installation and shut off the gas supply until it’s corrected.

There’s a bunch of stuff wrong with that plumbing job… but you should be able to shut off the feed valve to stop the flow of hot water. I’m more concerned about it not being properly vented though, if it’s a gas heater with no venting it’s poisoning your air.

Loooooooooooooooong Boi 🐧