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My exhaust vent came out of place on the top of my water heater and was venting fumes into the house. In a panic, I shut off the water heater knob to “OFF”. I had to leave town for a family emergency, and realized I did not turn the gas line off that connects to the water heater.Is this going to cause gas to leak into the house? Desperate for answers!!!

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    It will be fine, it is in OFF mode, so no reason for it to come one.
    – Traveler
    Commented Nov 23, 2022 at 7:02
  • For clarity, does your water heater have a metal control with two knobs, and you turned the little knob at the top of the control (marked OFF-PILOT-ON) to off? Not the big temperature knob at the front? Otherwise, do you have the newer kind with a big white box and only one knob? (If it's confusing, you could add a picture of a control to your question with the knob marked)
    – user71659
    Commented Nov 23, 2022 at 20:30

2 Answers 2

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There is a valve that works with the water heater to let gas flow into the burner when needed, when water cools down.

When you turned off the heater, that valve was also closed/not allowed to open. The gas shut off is a second valve that stops the gas flowing.

Best practice is to turn off both, but one or the other will do the job.

It is like with sinks. You have the tap to turn on/off the water and a second shut off valve usually under the sink to shut off the water also.

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There are two different possible issues here:

  • Main Burner

The gas flow to the main burner turns on and off based on the thermostat. Since the thermostat is turned to OFF, no gas will flow, as already explained in another answer.

  • Pilot Light

Traditional residential gas water heaters use a pilot light. This is a small flame that is always on. Gas cooktops used to do the same thing, but not for many, many years, as it was a waste of gas. However, water heaters (a) need to run totally unattended, (b) do not necessarily have electrical right next to them (unlike cooktops where electrical is available because kitchens are required to have a number of circuits anyway), (c) cycle periodically even if nobody is using much (or over a long time, any) water and (d) the little bit of heat from the pilot will, at least in theory, go into the water helping maintain the temperature. So a standing pilot on a water heater is still quite common.

The amount of gas used by a pilot light is very, very little. The question is whether the valve stays open all the time, assuming that there is a pilot burning, or whether the valve automatically closes if the pilot light goes out. I don't know the answer to that. You may be able to figure out based on the particular make/model of water heater, or someone else with more experience may have a definitive answer based on industry standard practices. Except during water heater replacement, the only time my water heater pilot had to be lit was when the gas company replaced the meter - and they took care of it for me. A few minutes of "pilot gas" would be of no concern at all. The concern might be if it goes for hours or days and accumulates.

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    Most such controls I've met have Of-Pilot-On settings, so if Off, the pilot is also off. Anything that isn't ancient also has a thermocouple on the pilot flame that shuts off gas if it's not hot.
    – Ecnerwal
    Commented Nov 23, 2022 at 16:38
  • The traditional 2-knob control doesn't have OFF on the thermostat knob, the lowest setting is VACATION. The vacation setting isn't off, it's a very low (~50 F) setpoint, so that the water in the tank won't freeze. OFF is only on the gas control knob. The newer electronic controls have only one knob that controls everything.
    – user71659
    Commented Nov 23, 2022 at 20:16

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