Supply valve to bath faucet doesn't stop water
I just moved into a house (built in 60s) and was about to replace a bathroom faucet. When I tried to turn off the faucet's hot and cold water supply valves, no matter how much I turned them, the cold water still ran fully and the valve started dripping slightly. The hot water slowed to a crawl but never fully stopped.
I suspect I should replace the supply valves with new ones? If so, I have a question about the shutting off the main water supply: We have a gas tank water heater. Next to it is the main water supply valve, a cold water supply valve, and the gas supply valve. Can I just turn off the main water supply valve or do I need to turn off the gas supply valve as well?