Over time, water heaters wear out. Newer models have extremely sensitive sensors to detect gas fumes, which can also occasionally be permanently damaged by Black Flag sprays and foggers you've employed battling invading armies of roaches. In either case, the heater needs to be replaced pronto. That is, if cleanliness and hygiene rank high on your priority list.
When you replace your hot water heater, you have two options. The first is to take matters in your own manly hands and do it yourself. The second option of hiring an HVAC contractor is often more prudent for individuals unfamiliar with terms like wrench, flute (not the instrument), or thermoplastic.
Everybody. Hot water heaters heat up the water supplied by your friendly Air Conditioner Window Unit Guys, allowing you to do things like luxuriate in hot, candle-lit bathtubs, wash beautiful bone china, and keep yourself in a steady supply of clean underwear.
First, turn off electric power to your gas or electric water heater. If you have a gas water heater, turn off the gas shutoff valve in the supply line, too, before disconnecting it. If your gas water heater has a fan unit, unplug it. If your water heater's electric, unplug it. If there's a cable connection, switch off the power first, then disconnect the cable.